What do you mean, “short of mass murder”? The Republicans have already passed a law that possibly kicks of 28 Million (possibly because nobody bothered to run actual numbers before passing it) Americans off their Healthcare, to Keep their promises of getting rid of Obamacare (though most People disgruntled with Obamacare wanted it fixed, not gotten rid off).
This is also Trump who just a short time ago orderd to bomb Syria, just because … who knows why, really.
Remember the run-up when the Republicans had 10 nominates for the candidate as POTUS? Well the Problem was not only that despite the Party leaders trying to rig things to not nominate Trump - it was that most of what Trump said was shared by the other 10. The racism, the bigotry, the hate towards the poor and slashing things for them, while giving tax breaks to the rich, the xenophobia, the courting-the-evangelicals things - all have been Mainstream Republican, esp. with the Tea Party showing up and forcing new purity tests.
Likewise, denying of Facts has been going on Long before Trump was sworn in - Republicans want to Profit more from climate denial than from preparing People against the climate Change effects, or creating new Jobs in solar/ wind. And Fox has been conservative/ pro-Republican for decades now, along with its infamous commentators.
Also Bush II won with Image of “Aw shucks I don’t know anything” - voters obviously don’t want experts (hey, since Facts are alternative or conspiracy, who Needs experts?)
The voters reward the Republicans every step of the way for decades, and Tea Party shocked them into more craziness and hate as being the winning formula.
Why should they Change? If they get the Donald upset, he has already threatened them when re-election Comes around. And at the Moment, he has the power to blacklist them from many positions inoffocially. But if they don’t say anything, they can Keep power and Money. Why should they stand up?
When was the last Point the Republican Party actually cared about/ did something that was good for the Country or the majority of the People? Not what they claimed, but when they did? Long before shutting down the whole Country for weeks in a fit of “toddler-stamping-its-feet” over Budget issues. (Though that is partly also your broken System - here, the old Budget doesn’t run out, it keeps going until the new Budget is passed, because it would be stupid to make the Country that vulnerable to petty tactics).