Mainstream Republicans
There's been much discussion about Trump's base, "mainstream Republicans," whether or not Trump followers (and Faux News) will eventually see the error of their ways, etc.
I postulate that, in spite of his low approval rating, Trump's base is each of the following:
1) a clear majority of the overall Republican Party base (not a small subset but the bulk of what is today's GOP base)
2) more rabidly supportive of Trump than the GOP base was of previous Republican presidents (a cult-like following that is more likely to act violently in response to opposition)
This poses a real dilemma for Republicans (be they in Congress, in media, or in the electorate) who would much rather have someone like Pence or Romney or Jeb Bush in the presidency. They can't risk alienating the bulk of their base.
Trump is truly a monster of the Republican Party's own making. Decades of Southern Strategy, dog whistling and more blatant hostility (toward POC, women, LGBTQIA+, immigrants, poor people, non-Christians, etc.), as well as jingoism, laid the groundwork for Trump and his following.
At the same time, an argument can be made and has been made (just recently in another thread, in fact) that impeaching Trump carries some potential risk for Democrats and the US as a whole. That's a more complicated argument and one I'm not completely dismissive of, but that's a whole other discussion and not one I wish to take up in this thread.