Everything comes back to Trump; imagine if they hadn't run him as their nominee for the 2016 election, and ended up with someone like Jeb Bush instead. Now realize that if Trump loses reelection, and for some reason decides not to run in 2024, the Republican party has almost nobody else like him; Jeb Bush for 2024 is a very real possibility.
I don't know about anyone else, but I'm not going to vote for Jeb Bush, or Mitt Romney, or any other member of the Republican establishment; so unless somebody like Dan Crenshaw gets the nomination, or another outsider like Trump, the Republican party is as good as dead in my eyes.