There were always kooks. One or two senators are not the reason the entire atmosphere changed, especially when the majority only needs a handful of minority senators to get laws passed. Citing the extremists is not the right argument here, IMO. Unless I'm misunderstanding you.
Hawley isn't an outlier kook though like AOC and her Modern Monetary Theory, most of the GOP supports Hawley. He's an extreme that proves the center has shifted. McConnell isn't much better, he's just smarter at it.
"Everything got more polarizing" is probably the best answer. Trump and his fiercest critics are both to blame for it, though people on each side of the aisle will think that the other is "more to blame" for it.
The difference is polar Dem policies are often
for the people and polar Rep are more often based on entirely fictitious alienation of dems. AFAIK, Trump was the first person in major public office whose entire agenda was doing the opposite of the other side, no matter the topic. He didn't start the demonization though, he just successfully capitalized on it. I don't who started it, but Rush Limbaugh played a large role.