I think this is pretty obvious if you compare Trump's support among Conservatives with that among Republicans.
Conservatives vote 85-15 GOP so that's not a problem anyway.
And the upshot themselves said there are more white voters than people believe, and these missing whites have come for Trump and the GOP, see them always overperforming the polls after Obama left the ballot.
Conservatives will vote 85-15 Republican no matter who is the Republican nominee.
President Trump's behavior as President is so erratic as to be indefensible. He has made some wild appeals, but he has accomplished nothing. President Obama could get more done with Republican majorities of both Houses of Congress. I'm going so far as to say that one will be shown as an example of how to be President and the other on how to not be President.
I do not expect President Trump to complete his term of office. First, he is at risk of death or extreme disability due to his age and poor health habits. Meat burned to a crisp itself creates a risk of cancer. Obesity and a lack of exercise put him at risk of a stroke or a coronary. Senile dementia is a risk for anyone his age, although the limited vocabulary could reflect the tendency of people in the real-estate business to speak in clichés characteristic of the business. Second, he may find the job beyond his ability -- way beyond his ability. Third, should he lose one or both Houses of Congress, then such could be a complete rebuke to him and make the Presidency impossible. He has cut and run before.
Forget impeachment. Even if twenty Republican Senators want this President gone, Democrats still can exact some influence on the process by holding an effective veto on the Vice-President. Count on Democrats putting up much resistance to efforts to transform America into a Christian and Corporate State -- the sort of place in which labor unions, abortion, contraception, and evolution are banned, and in which the tax burden falls on the non-rich to support a government that exists largely to enforce the will of the rich.
I trust the Secret Service to be watching any threat of violence against him closely -- but it can't guard against blood clots, malignancies, or prion diseases. Democrats running for House and Senate seats will be running against Donald Trump.