It didn’t help Mr. Trump’s case that Kurt Volker, the former top envoy to Ukraine and one of the Republicans’ own witnesses, on Tuesday afternoon dismissed the claims of corruption by the Bidens as conspiracy theories.

Without any substantive defense of the president’s behavior, Republicans did all they could to deflect. They called the hearings a circus. They demanded to know the identity of the whistle-blower — even though they previously complained that he had not listened to the July 25 call, and two people who had heard the call were sitting right in front of them. They criticized the media.

They continued to push the idea that Trump is genuinely interested in rooting out corruption. That was never plausible to begin with. But it became even harder to sustain in light of the fact that anti-corruption measures were on a list of talking points prepared for Mr. Trump both times he spoke with Mr. Zelensky, and both times he failed to raise the issue at all. (And as Representative Eric Swalwell noted, the Pentagon had certified that Ukraine had met its anti-corruption requirements for receiving the military aid before Mr. Trump withheld it.)

And Stephen Castor, the staff lawyer for the Republicans, darkly insinuated that Colonel Vindman harbored dual loyalties to the United States and Ukraine, because a Ukrainian official had repeatedly offered him the job of secretary of defense. Colonel Vindman acknowledged the offers and laughed them off; the Ukrainian official later said he had been joking.

It was a particularly repulsive line of attack in light of Colonel Vindman’s opening remarks, in which he addressed his father, who escaped the Soviet Union with his family when the colonel was a young child, in the hope of a better and safer life in America. “Do not worry, I will be fine for telling the truth,” Colonel Vindman reassured his father. When Representative Sean Patrick Maloney later asked him why he had said that, he replied: “This is America. This is the country I’ve served and defended. That all of my brothers have served. And here, right matters.”

The gallery burst into applause while Republicans sat and stewed. Perhaps they were reflecting on another part of Colonel Vindman’s opening statement, in which he said that the testimony he was about to give “would not be tolerated in many places around the world,” specifically Russia. If the exasperated Republicans had their way, it wouldn’t be tolerated here, either.