The thing that finally pushed Senate Republicans over the edge was child molestation. They were willing to ignore Alabama Senate candidate Roy Moore's declarations that Muslim Americans should be barred from public office. They were willing to brush aside Moore being booted from his day job not once, but twice for declaring that he, and not higher courts, was the final interpreter of American law. When he spouted theories about our nation's first non-white president being a secret foreigner few Republicans had a thing to say about it. The man peddling hate speech against LGBTQ Americans was fine; it took a graphic description of an apparent attempted rape for the party elders to finally jump ship.
So it is not too surprising that, when asked why they rightly believe Roy Moore's multiple accusers when they did not believe 20 or more women who accused Donald Trump of assault during his own campaign, few answers are forthcoming and those that are are unconvincing.
Sen. Richard Burr (R-N.C.) argued that the “sheer volume and the level of detail that’s been provided” by Moore’s accusers “draws enough conclusion” for him to say the Alabama Republican ought to withdraw from the race. As for whether Trump’s accusers should be believed, Burr said he was “only addressing Roy Moore.” [...]
Sen. Mike Rounds (R-S.D.) said he believes the women accusing Moore of sexual misconduct but threw his hands in the air when asked about Trump’s accusers. [...]
Sen. Steve Daines (R-Mont.), one of four senators who endorsed Moore’s campaign, walked away without saying anything when asked if Trump’s accusers deserve the same benefit of the doubt as the women who accused Moore of sexual assault.
Then there's Mitch McConnell himself, who reverted to his terrapin ways when asked about Trump's own sordid history.
So I don't think we should get too attached to the idea that the nation's top Republicans finally, at long last, have found some lower bound of candidate behavior under which they are no longer willing to go. The abandonment of Moore while still polishing Trump's shoes suggest that their morality remains, shall we say, transactional at best.