Buddy sent me this link. I'm a professional social scientist who works in this area. There's a lot, but I'm gonna focus on two things.

1. Donald Trump, 2) Slanted elections

1. Donald Trump. He has been the de-facto party leader since his nomination for the presidency in 2016. He has repeatedly endorsed and encouraged violence among his supporters, culminating with the January 6 Capitol Attack. And he hasn't stopped. (The opinions and beliefs of leadership trickle down to shape the beliefs of their supporters--see an example here. Despite many of their misgivings, one of three things happened to Trump's GOP opponents: -A) They voluntarily left elected office (Bob Corker) -B) They were punished for criticizing him (Liz Cheney), or -C) They fell in-line (Ted Cruz). Those who left the GOP or were forced out have been replaced by more extreme leaders yet--folks like Marjorie Taylor Greene. Few left in the GOP openly challenge Trump because they've seen what happens to those who do. So there's no one of much influence within the GOP capable of leading a credible anti-Trump charge.
2. The GOP is better shielded from the electoral consequences of extremism than Democrats. Owing to aggressive partisan gerrymandering after Republicans swept statehouses in 2010, MANY state and U.S. House districts were drawn to maximize the number of uncompetitive elections that would all but ensure Republican majorities. You see this in many states that are very competitive at the state level like North Carolina and Wisconsin, but Republicans have locked up enough statehouse seats to retain control of legislatures, even when most of the state's vote went to Democrats. Uncompetitive elections mean that incompetent, corrupt, and extreme candidates who alienate most voters can still defeat moderate consensus-builders. What happens is Democrats have to run candidates with exceptional cross-appeal (i.e., moderate consensus-builders) if they want even slim electoral wins. Meanwhile, Republicans can hold onto those majorities without having to moderate.