REPUBLICAN SENATORS who voted Friday to suppress known but unexamined evidence of President Trump’s wrongdoing at his Senate trial must have calculated that the wrath of a vindictive president is more dangerous than the sensible judgment of the American people, who, polls showed, overwhelmingly favored the summoning of witnesses. That’s almost the only way to understand how the Republicans could have chosen to deny themselves and the public the firsthand account of former national security adviser John Bolton, and perhaps others, on how Mr. Trump sought to extort political favors from Ukraine.

The public explanations the senators offered were so weak and contradictory as to reveal themselves as pretexts. Sen. Lisa Murkowski (R-Alaska) said she weighed supporting “additional witnesses and documents, to cure the shortcomings” of the House’s impeachment process, but decided against doing so. Apparently she preferred a bad trial to a better one — but she did assure us that she felt “sad” that “the Congress has failed.”

Sen. Lamar Alexander (R-Tenn.) said the case against Mr. Trump had already been proved, so no further testimony was needed. But he also said, without explanation, that Mr. Trump’s “inappropriate” conduct did not merit removal from office; voters, he said, should render a verdict in the coming presidential election. How could he measure the seriousness of Mr. Trump’s wrongdoing without hearing Mr. Bolton’s firsthand testimony of the president’s motives and intentions, including about whether the president is likely to seek additional improper foreign intervention in that same election?

Sen. Marco Rubio (R-Fla.) echoed Mr. Alexander’s illogic, only he lacked the courage even to take a position on whether Mr. Trump had, as charged, tried to force Ukraine’s new president to investigate former vice president Joe Biden, or whether that was wrong. Sen. Ben Sasse (R-Neb.) managed to be even more timorous, telling reporters that “Lamar speaks for lots and lots of us” and refusing to elaborate.

So cowed are most of those “lots and lots” of Republicans that few of them dared to go as far as Mr. Sasse. Some have echoed the president’s indefensible claims that there was nothing wrong with the pressure campaign. Their votes against witnesses have rendered the trial a farce and made conviction the only choice for senators who honor the Constitution.

Americans who object to Mr. Trump’s relentless stonewalling and Republicans’ complicity can take some comfort in the prospect that most or all of the evidence the White House is hiding will eventually come out. A reminder of that came Friday in a New York Times report about Mr. Bolton’s unpublished book, which describes how Mr. Trump ordered him last May to tell Ukrainian President Volodymyr Zelensky to meet with his personal lawyer Rudolph W. Giuliani. Mr. Giuliani said publicly at the time he wanted to induce Mr. Zelensky to investigate Mr. Biden because it would be “helpful to my client,” Mr. Trump.

That report underlined the cringing shamefulness of the Republican decision to block Mr. Bolton’s testimony — and there will surely be more reminders in the weeks and months ahead. We can hope only that voters who wanted that evidence to be heard in the trial will respond by showing incumbent senators they are a force to be reckoned with, as much as the bully in the White House.

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