In other words, for 40 years after the fall of Richard Nixon, it was easy to proclaim that character mattered and still pull the lever for a Republican. In 2016, however, a commitment to virtue became costly. In the battle between virtue and politics, virtue lost, and it’s losing still. I’d like to dwell on two reasons. The first is easy to name — negative polarization. The Pew Research Center has outlined the undeniable growth in enmity between left and right. The parties are not only more ideologically extreme, but partisans are now motivated mainly by antipathy toward the other side.

This phenomenon explains why reluctant Republicans would pull the lever for Mr. Trump even if he was their “last choice.” They were voting in perceived self-defense, and he fights hard against the people they dislike the most.

But this doesn’t entirely explain the curious unwillingness to face bad facts or to critique the most baldfaced lies. Talk to folks in Trump country, and you quickly understand that most of them don’t just want to win, they also want to be good. They want to be proud of their movement. They see themselves as good people, and they want to root for a good man.

The desire to think the best of Mr. Trump combined with the deep distaste for Democrats grants extraordinary power to two phrases: “fake news” and “the other side is worse.” “Fake news” erects a shield of disbelief against the worst allegations and allows a person to believe that Mr. Trump is better than he is. For too many Republicans, every single troubling element of the Russia investigation — including multiple administration falsehoods about contacts with Russian officials — represents “fake news.”

This week’s news can be waved away. Mr. Manafort’s conduct had nothing to do with the campaign, they argue, even though the investigation continues and even though Mr. Trump showed terrible judgment in bringing him on the team. Mr. Papadopoulos was a nobody, they say, even as his guilty plea outlines multiple contacts with a “campaign supervisor” who seemed to encourage him.