Because polling data and Trump's approval rating do not tell the whole story.

As right-wing political commentator Ben Shapiro is fond of saying, two things can be true at once: It's entirely possible to both despise President Trump's character, bombastic personality, and divisive rhetoric AND simultaneously appreciate what he has done and is trying to accomplish policy-wise.

Consider the following from a conservative's perspective:

• Trump's signature campaign promise was to get tough on illegal immigration, and he has done exactly that. Illegal immigration has always been a major concern for the right. Even though his "zero tolerance" policy is heavy-handed (or an outright human rights violation if you're on the left), it has sent a clear, unambiguous message to Central- and South American countries that the US/Mexico border is no longer an open thoroughfare for entering the United States illegally.


• The Tax Cuts and Jobs Act dramatically reduced corporate income taxes, which was previously the highest tax rate in the industrialized world. Regardless of whether you think this is good or bad for the economy, it has been a Republican policy wish for literally decades, and it finally got done under the Trump administration.


• The terrorist group ISIS, which was a major Middle East security concern that plagued the Obama administration, has nearly vanished from world headlines. The U.S. had a large role to play in that victory.


• US/Israeli relations are the best they've been in decades, and the Trump administration has been extremely friendly towards the Jewish state. Moving the U.S. Embassy to Jerusalem is widely seen as huge positive step among conservatives and Israel's supporters -- especially among Christian conservatives. Other countries have since followed America's lead.


• Trump held a peace summit in Singapore with North- and South Korean leaders to discus nuclear disarmament of the Korean peninsula. It was the first time in history that North Korean and U.S. leaders have met face-to-face for talks. And while it remains to be seen what will come of them (North Korea has reneged on its promises in the past), it is nonetheless historic. North Korea has already destroyed some military outposts along the border, and has begun removing land mines from the DMZ.


• Trump has appointed and continues to nominate conservative judges to federal courts and to the U.S. Supreme Court. This is another campaign promise he has fulfilled. Conservatives who oppose Trump still enjoy the fact that the conservative tilt to the federal judiciary will outlast his legacy as president.


• Trump is constantly fighting back in the culture war. Despite his over-the-top rhetoric and criticism of "fake news", conservatives have been broadly troubled by left-wing identity politics and what they perceive to be pervasive liberal media bias for quite some time. This is the one place where Trump's rhetoric is a win for him politically among conservatives. Even many people on the right who don't support Trump's presidency tend to agree with him on this, even if they take everything he says with a grain of salt. Some conservatives argue that this reason alone is what got him elected in the first place.

Please note that this is not an overt argument in support of Trump. I am merely laying out the case for why conservatives specifically have not disowned him outright. If you could separate Trump's character and the garbage he craps out on Twitter from the way he has actually governed as President, his policy agenda and accomplishments to date read almost like a conservative dream come true.

Also note that there are a lot of policy disagreements among conservatives as well that work to temper their support; his belief in tariffs and his cozy disposition with world dictators are notable examples.

The bottom line is that, unlike with previous presidents, you can't conflate Trump's popularity and his performance as a governor. As it stands now (December, 2018), it does not appear likely that he will be reelected. But it all depends what happens between now and then, and on who the Democrats pony up for the 2020 race.

It may seem like a tautology, but Trump is popular where he is popular. Such is the case with divisive figures. In order to remain in office, politicians in those areas where Trump is popular feel the need to heed the will of their own personal constiuency and embrace Trump.

To be fair, an opinion I share is that some of the popularity that Trump receives in no small part comes from how unpopular he is where he is in fact unpopular. That is to say that those who are ardent Trump supporters like him more because of who he upsets and how he goes about it. People running for office in these areas are more than likely going to embrace and hope to emulate the Trump presidential style because it makes them more popular where it actually matters for them. Someone running for congress from Oklahoma probably couldn't care less what Trump's poll numbers in California are. If he is popular in their district then they will continue to support him.

Further, according to the most recent Gallup Poll Trump maintains 89% job approval within the Republican party. By contrast, Barack Obama's job approval for Democrats in his last week in office was 95% which isn't too far above where Trump is. The two have drastically different approval ratings from Independents, with Trump having 39% most recently and Obama holding 61% in his last week.¹

It is highly possible that the so-called "Never Trumpers" in the Republican party are in a tight spot, since they seem to be completely out of step with the rest of the Republican electorate. Many have already fled the Republican party which in cases of states with closed primaries means they have already abdicated any responsibility of helping the party choose the next nominee. Trump's style of always counter-attacking against perceived slights helps to keep all except the most outspoken against him in the party silent out of fear of retribution. This doesn't mean that those who approve of the job Trump is doing wouldn't support another Republican nominee more, but the current signs point to the Republican electorate being solidly behind Trump.

But will such a scenario repeat itself for 2020? Probably not, given the immense popularity of the most likely Democratic candidates, be that Elizabeth Warren, Beto O'Rourke, or Joe Biden.

I think you could be overestimating those politicians' overall popularity. Donald Trump wasn't supposed to be elected the first time around. I think you make a good point in that Clinton's unpopularity probably did help get him elected, but now that he's in office he is delivering on things that Republican voters want, so why would they switch?

_{1- For completeness, Trump has 6% job approval from Democrats and Obama had 14% from Republicans.}

Because they can't credibly convert Trump supporters.

The popular narrative is that Donald Trump's election represents some sort of "whitelash" against Democrats, Obama supporters, human decency, etc. But rich racist white people voted for Romney and McCain too.

Trump clearly won on the backs of working-class voters. Of pretty much all races (outperformed the last two Republican candidates among both Hispanics and African Americans). How an outsider managed to capture such a large and valuable demographic is an interesting question in its own right, but I'll give you the Occam's Razor: that demo was being ignored by both major political parties.

Think about it. 50 years ago pretty much all e.g. sitcoms were about working class people. 20 years ago most still were. Now almost none of them are. Those people have gradually been excluded from cultural relevance. Jobs have moved, and towns have died. Industries have changed. If anyone in Washington cares, it's awfully hard to see it from podunk.

Now along comes this guy who says, hey I'm for you, I'm going to fight for you, I'm going to focus on you unlike these other yahoos...

And the sad part, for those who don't like President Trump, is that nothing, nothing has changed about that dynamic since the election. Trump is still the king of his domain. Democrats aren't even an also-ran. They haven't made the first attempt to court those people. They have dismissed them as racists and/or opioid addicts. And there are plenty of Republicans who are going to say eh, I don't like him, but I'd still vote for him ahead of the other side.

On the marginalization of working class voters

There's been some discussion about this in the comments. So to show what I mean, here's an incomplete list of questions that seem (to me, based on living in the Midwest) to be on the minds of working-class voters, no particular order:

1. What if the evidence for global warming is faked, or even just misinterpreted?


2. What if a loss of manufacturing jobs destroys American small towns and the culture they represent?


3. What if that culture is further threatened by waves of immigrants?


4. Our politicians seem to be an entrenched bureaucracy of people who could broadly be defined as "not us". They're not even pretending to care about us anymore. What do we do now?

In terms of discussion on the national stage, the conversation is pretty lopsided. I frequently see point 4 brought up except the people doing so... aren't exactly the salt of the Earth. Points 2 and 3 are always couched in terms of money (we'll throw them a bone sometime! maybe!) and racism, respectively. It's never talked about in terms of culture/way-of-life. Few are willing to risk the labels that come with the media consensus on climate change. Well, except that one guy...

And I'm frankly not sure what to make of all of this. Because while I'm from a small town, I went urban a long time ago and never really looked back. I'm educated, liberal (compared to them), etc. I'm one of the people they complain about. I've become one of the people they complain about. And I like the new culture better than the old. But I also know people. Good people. And I just don't see a crusader for their culture in e.g. Mitt Romney.

Addendum #2: Why we can't have nice things

I should thank the OP. This question is the gift that keeps on giving. In response to my 4 points above, a commenter responded with

1. What if it's not? What if airplane jet trails were really chemicals designed to control the population? What if our leaders are actually lizard men? What if nonsensical what-if-questions were actually pointless?


2. Better not vote for free-market Republicans, because Capitalism says you should find new jobs or fade away. Fun fact, the current administration ended programs to help workers displaced by automation get training for in-demand fields.


3. People who immigrated to the US are now worried about immigration? That's just funny.


4. Probably not vote for billionaire con men.

Think about how that sounds to the average middle American. Think about the message it conveys (regardless of whether or not it's true): you're too stupid to know what's good for you. Think about what the most likely response is. Saying that to someone is not going to make them meekly back down. It doesn't even matter if you're right. You think they're going to listen to someone who's belittling them? They're going to hate you, and they're going to react to you by allying themselves with something they know you hate. You (yes you) are actively encouraging people to vote for Trump. Please, please stop.

There's an old English proverb that goes, "In for a penny, in for a pound." It is an example of the sunk cost fallacy, basically saying that once we put some effort/money/worthwhile thing into a cause that we can't easily reverse, our tendency is to follow through to the end, for fear of 'wasting' that initial effort/money/worthwhile thing.

The Republicans spent boatloads of political capital and trashed decades of a good reputation for Trump when they saw he could get the things that they wanted from government, and he's been fairly successful at doing so. Unfortunately, Trump, like any good mob boss, requires loyalty and a willingness to get dirty on his behalf, and treats anyone who voices disagreement as an enemy. And as the midterms show, Republican enemies of Trump don't get re-elected. And as for getting dirty on his behalf? There seem to be plenty willing to do so.

So where does that leave us at? The Republicans aren't going to give up on Trump en masse, because that would mean that several of them will likely be charged as accessories to one or more crimes. And they're the only ones with the power to prevent that ending.

Elected Republicans have to support Trump, because the people who elected them support him.

Trump may be unpopular in general, but among Republican voters he is not just popular, but very popular. Like second historically only to Bush at the start of the second Gulf War. Those kinds of numbers.

The US is a country where the vast majority of elected officials now live in "safe" districts. This means the primary is a much more dangerous election to most Republicans than the general election. Heck, even in a tossup district, you still have to first win a primary where the only voters are Republicans. Attacking the head of your own party when his approval is north of 85% (which is likely higher than your name recognition, let alone your approval rate), is a great way to commit electoral suicide.

Effectively, with that kind of approval among the Republican electorate, an elected Republican's choices are support Trump, or be replaced by someone who supports Trump. That's it.

There's no hard proof for "why", but the following are all reasons stated at one time or another. They aren't mutually exclusive.

1. High level Republicans don't want to antagonize Trump due to negative consequences from him.




2. High level Republicans don't want to antagonize Trump due to negative consequences from their electorate who are Trump supporters.




3. High level Republicans don't want to antagonize Trump due to negative consequences to the party from infighting. Both as far as morale, and opportunity cost (an hour/a dollar spent infighting is an hour/a dollar not spent opposing the other party).




4. Inevitability. Trump demonstrated that he can beat any even most formidable R opponents in primaries in 2016. It may very well be that people just take it for granted he's inevitably going to win 2020 primaries, so why spit upwind?



5. 
   

   Trump actually delivered on many things (see Wes Sayeed's excellent answer for a list). Arguably, more and more important things than R presidents before him. Bush may not have had any scandals and got re-elected, but what exactly did the conservatives get out of it as far as political achievements? (good question to ask on this site, but my impression is "not much in second term").

   
   
   

   To paraphrase, if:

   
   
   

   P(T,E) = "probability of Trump winning general election"

   
   
   

   P(T,A) = "probability of Trump delivering things Rs want"

   
   
   

   P(R,E) = "probability of Trump replacement winning general election"

   
   
   

   P(R,A) = "probability of replacement delivering R agenda"

   
   
   

   the calculation is as follows: is P(T,E) * P(T,A) < P(R,E) * P(R,A) ?

   
   
   

   While you can make legitimate arguments that P(T,E) is less than P(R,E) (someone else is less likely to lose a general election), you can ALSO make a legitimate argument that P(T,A) is far bigger than P(R,A) - some RINO Republican like Romney governing like Democrat Lite wouldn't really be much of a win for Republicans as far as agenda.

   
   


6. 
   

   Somewhat linked with 4, there are downsides to a non-Trump Republican winning 2020 General elections.

   
   
   

   Due to reversion to the mean, that would almost guaranteed assure 2024 Democrat win (and 2022 Democrat midterm win). Conversely, Democrat winning in 2020 may cause that to revert ala 2014.

   
   
   

   Having an effective (as far as delivering agenda) R President is obviously worth such downsides.

   
   
   

   Having an ineffective R president may not be.

   
   



7. Trump demonstrated in practice that he can win. So, while you can make reasonable argument that he'd be more likely to lose in 2020 than 2016, you can also make reasonable arguments that he will manage to win 2020 more than a competing R candidate despite his weaknesses.

Damage to the Party

Like the asker suggested, Trump could be posing damage to the Republican brand. Anytime Republicans oppose Trump on an issue, he publicly disrespects them. He has attacked current and former Republican politicians, pundits, party supporters, and members including John McCain, Ted Cruz, Paul Ryan, Mitch McConnell, Jeb Bush, Chris Christie, Steve Bannon, Glenn Beck, Jeff Sessions, Jeff Flake, Lindsey Graham, George H. W. Bush, George W. Bush, Rand Paul, Rick Perry, Mitt Romney, Ben Carson, Carly Fiorina, Nikki Haley, John Kasich, Megyn Kelly, Karl Rove, Marco Rubio, Charles Krauthammer, the Koch Brothers, the Fox News network, Lisa Murkowski, Sheppard Smith, Scott Walker, and Robert Mueller. Trump has hired and fired some prominent Republicans within the party establishment, including former RNC communications director Sean Spicer, former RNC chairman Reince Priebus, and former Republican senator Jeff Sessions. Some have said the 2018 mid-terms would be a referendum on the public's sentiments towards Trump, and in 2018, Republicans lost the House of Representatives (and by a wider margin than projections predicted) for the first time since 2008, and lost ground on many gubernatorial seats.

There have been many articles speculating that Trump is doing long-term damage to the Republican brand 1 2 3 4.

Beware of Spoilers

One consideration missing from other answers is the effect of spoilers during primaries. In the 2016 Republican primary, there were 12 candidates who ran in the primary, and 5 more in the mix who dropped-out before the primary. By most peoples' view, Trump was most unique among the field, whereas many other candidates were part of the tea party establishment, who either held public office as a Republican, or campaigned in previous Republican presidential primaries; and many of them had extremely similar policy positions and messages. In other words, the other 16 candidates were virtual spoilers or clones of each other. This put Trump in a position to dominate many of the earlier primary races, and this advantage of running against a field of clones would persist until the final three candidates (it's fair to say, at this point, that Ted Cruz and moderate John Kasich were as mutually different from one another as they were from Trump). It's been argued that towards the end of a primary process, some party members will get behind the candidate in the lead and give that candidate a big push so that they have big momentum coming out of the primary. If this is true, Trump's lead in pledged electors towards the end of the primary persuaded Republicans to support him more strongly during his final stretch against Cruz and Kasich.

The point I'm trying to make about spoilers isn't just about 2016, though. The question is... in 2020, will Trump have the same kind of advantage granted by spoilers, or could he have a disadvantage in the form of spoilers? It's always possible that the 2020 Republican primary field could be 4 candidates very similar to Trump (like Steve King, Roy Moore, Matt Gaetz), and only 1 candidate different from Trump's style (like John Kasich, Jeff Flake, or Susan Collins). Part of the reason that I propose this possibility is that more and more Republicans are emulating Trump's politics, meanwhile established party insiders rarely contest the seat of a sitting president. This could mean, in theory, lots of Trump clones, but very few establishment types (like Orrin Hatch, Mitch McConnell, Chuck Grassley). So... Trump's viability in the 2020 primary might be at risk, but there are no guarantees of that either.

What Else Can Republicans Do?

There are basically two kinds of recourse I know of to remove Trump from office, which are defeating him in a 2020 party primary, and impeachment. Successfully impeaching Trump would required something like 18 Republican senators voting to convict. Any Republican senator in a heavily red state who voted to convict Trump could expect to face certain defeat in their next re-election. Even in swing states, it is certain that they would not win their next party primary as long as Trump's approval among Republicans is around 89%. Impeachment is not a realistic possibility, because political self-interest will trump any evidence of a crime. Another way of removing the president (but this is not entirely up to the RNC, as per the question) is by invoking Section 4 of the Twenty-Fifth Amendment. This would require the action of the Vice President, and the collaboration of the majority of another body (I wonder if its sufficient to have the VP and the majority of the House of Representatives).

Whenever the Vice President and a majority of either the principal officers of the executive departments or of such other body as Congress may by law provide, transmit to the President pro tempore of the Senate and the Speaker of the House of Representatives their written declaration that the President is unable to discharge the powers and duties of his office, the Vice President shall immediately assume the powers and duties of the office as Acting President.

Fundraising

The most likely route to remove Trump from the Republican brand is to defeat him in a 2020 party primary. Another relevant battleground for this primary is going to be fundraising. A challenger to Trump's seat is going to need to gain favor with prominent Republican donors, and attempt to also court traditionally Democratic donors who want to enable a Trump defeat.

Here are some top relevant donors in the 2018 election cycle according to opensecrets

Top organization Republican donors: Las Vegas Sands, Adelson Drug Clinic, Uline Inc, American Action Network, Senate Leadership Fund, Blackstone Group, and Republican Governors Assocation.

Top organization Democratic donors who also donate substantially to Republicans: None. Some contribute very small amounts to Republicans.
Top Conservative or Moderate Super Pacs: Congressional Leadership Fund, Senate Leadership Fund, New Republican PAC, America First Action, DefendArizona, Club for Growth Action, With Honor Fund, National Assn of realtors, Patients for Affordable Drugs Action

Top PACS who contribute substantially to Republicans (all of these contribute to Democrats as well): National Beer Wholesalers Assn, AT&T Inc, Northrop Grumman, National Assn of Realtors, Sheet Metal Air Rail and Transportation Union, American Bankers Assn, Operating Engineers Union, Credit Union National Assn, Lockheed Martin, etc.

Top Republican individual donors: Sheldon Adelson, Richard Uihlein, Steve and Christine Schwarzman, Kenneth Griffin, Jeff Bezos, and Timothy Mellon.

Top Democratic individual donors who also contribute to Republicans: Michael Bloomberg, Thomas Steyer and Kathryn Fahr, Donald Sussman, James Simons, George Soros, Fred Eychaner, and Deborah Simon.

Although the Koch Brothers do not show-up in any of these lists by name, they are also understood to be a consistently large Republican donor, sometimes in amounts of hundreds of millions of dollars.

Any challenger to Trump will have to lobby the top donors for their support. In the case of the Koch brothers, the sparring between Trump and the Koch brothers may motivate them to back a different candidate. Jeff Bezos is also not likely to back Trump in 2020, due to souring relations, but he was a big backer in 2016. Michael Bloomberg's opinion of Trump may lead him to back a Republican challenger (although he's shown more interest in actually running against Trump in 2020). Trump's attacks on George Soros make it plausible that Soros could back a Republican challenger. Sheldon Adelson seems to be a steady supporter of Trump. While Richard Uihlein has consistently backed MAGA Republicans like Roy Moore, it seems that he may be getting tired of backing losers and may be rethinking who he gets advice from (Uline Inc will also use its money in the same way). Thomas Streyer supports impeachment of Trump, so he will probably support anyone who can credibly challenge Trump. Donald Sussman donated big money to the Clinton campaign to oppose Trump, so he might support a 2020 challenger. American Action Network has been a big Trump supporter. AT&T looks to be at odds with Trump, but they also paid $600,000 to Michael Cohen.

Support of Voters

Anything the RNC does to subvert the Trump administration is likely to incur backlash from the party's voters. Before taking its ultimate action (impeachment or whatever else), the party would first need to launch a substantial public relations campaign to become the voters' higher priority in relation to supporting Trump. The most prominent messaging system between the RNC and Republican voters is Fox News; so Fox News and its owner Rupert Murdoch are in a position to pick the winner of this fight. Fox News's coverage of Trump seems to be consistently supportive of him, barring a few exceptions out of thousands of hours of coverage. However, although Rupert Murdoch has a pretty close relationship with Trump, there is also tension within it 1 2. If Murdoch ever decided to shift Fox News coverage in a direction that prioritized the RNC over Trump, it could eventually pave the way for a big move by the RNC against Trump.

What you asked is very near opinion, so I will use my own opinion as an example. Keep in mind that I am using my opinions as an example, not to "support Trump" but because I think it shows a good example of why Republicans as a whole do not work towards his removal.

At the last election, I did not vote for Trump, though I do not consider myself Republican or conservative, by traditional means, and I even voted for and mostly liked Obama. However when voting, and during the run-up to the election, I was basically in the "Anyone but Clinton" camp. I am still happy that Clinton didn't win.

Now it's a couple of years later, and I am overall happy with Trump's performance as a president. I do wish for a new amendment to the constitution that says President's can't have social media accounts. I do wish he would shut up sometimes, but as far as policy goes, what has gotten done, and what he has worked for is mostly in line with my ideals. Not all of it, but most, and I am happy with that.

In order for someone to replace Trump, they would have to have the same ideals and ability to get things done, that I want done, while at the same time not looking so terrible on social media.

You would be very hard pressed to "sell" me a democrat at all, right now. Even another Republican would take a very special mix.

Do I support Trump? Not really, but I would rather have him than Clinton, probably another Democrat, and likely any Republican. I don't like him, but things are getting done. That's much better to me then nothing getting done.

So if the Republican party was to "oust" Trump, who could they offer in his place to keep my vote.

He has an overall 45% approval rating 1
Bush was at 37% 2
Obama was at 46% 3

Say what you want, he seems to have some support.

Something not mentioned in the other answers is that...

There are only two parties in the US

If the Trump loses in 2020, which is far from certain, the Republicans will simply have to work to regain power in 2024 or 2028.

Consider, for a moment, the viewpoint of the wealthy entities that provide funding for the lobbying organizations that currently influence (and to a certain extend, control) policy in Washington. From the viewpoint of most lobby groups, Democrats and Republicans are almost the same. Thus, they really don't care who is in power, just as long as they fund both sides during elections.

So the power behind all candidates doesn't seem to care if Trump is in power or not, so the Republicans also don't care.

And considering how similar Democrats and Republicans are from the viewpoint of the powerful entities that fund lobbying organizations, it is largely irrelevant who holds power.

Trump's unpopularity stems not so much from his actions, as his abrasive NYC personality. New Yorkers tend to be brusque and abrupt in general, a byproduct of the hectic environment they live in. Trump personifies and in some cases amplifies the less pleasant aspects of that.

So far, his administration has done well in keeping the campaign promises he made - more than a typical president. Many of those promises were nonpartisan, to the benefit of everyone, such as lowering unemployment. And, so far, he hasn't taken any actions that have had a negative impact on a large number of citizens... like Obamacare sending heath care costs through the roof. The tariffs he put in place are designed to persuade other nations not to tax US goods in an inequitable manner, and they appear to be implementing that very persuasion. The EU has already agreed to modify it's taxes, and China is showing signs of making long overdue changes.

While Trump may offend some people, he hasn't hurt the nation economically, and that's what really matters to voters in the end. If you look at the critique of Trump in the media, most of it is fairly superficial, a good deal of it is somewhat contrived or exaggerated - catering to an audience predisposed to believe only bad things about Trump. I was no fan of Obama after he sent my health care bill through the roof, but I never thought that justified removing him from office.

If you ask why the Republicans don't get rid of Trump, it's because there really isn't anything in what he has done, that calls for removal. Those of us who were around in the Nixon era remember the chaos that followed his resignation. Think long and hard before going that route... a lot of unintended consequences.

The closest parallel I can find is the Clinton/Lewinsky affair. No, that wasn't conduct becoming of a president. However, like Trump's acerbic remarks, that situation didn't materially affect the things that are truly important to most citizens: the state of the economy, and how well their personal financial situation is going. And it comes down to: better the devil you know, than the devil you don't know.