To understand the courage that witnesses like Marie Yovanovitch have shown during the Ukraine investigation, it’s worth looking back on a couple of the other signature moments of the Trump era.

One was in the summer of 2016, when James Comey, then the F.B.I. director, faced an uncomfortable choice. He and his colleagues had concluded that Hillary Clinton should not be prosecuted for using a private email account to conduct government business. Her conduct was sloppy and inappropriate, but it was also fairly common and not close to being criminal.

Still, Comey knew that Republicans would vilify him for his decision not to prosecute. They would portray it as partisan, rather than what it was: a straightforward application of the law. And Comey prized his reputation for appearing to be above partisan politics.

So he looked for a way to dilute the criticism. Instead of simply closing the Clinton investigation, he gave a news conference blasting her. Doing so violated Justice Department policy, but also ensured that the subsequent criticism of Comey would come from both Democrats and Republicans. Comey, in short, put a higher priority on avoiding the appearance of partisanship than on doing the right thing.