TWO VETERAN U.S. diplomats on Wednesday told a compelling story of how U.S. policy toward Ukraine was undermined and corrupted to serve President Trump’s personal political interests. For years, they testified to the House Intelligence Committee, the aims of the United States had been to help Ukraine resist armed aggression by Russia and to press it to tackle endemic corruption. That abruptly changed earlier this year.

“The security assistance we provide is crucial to Ukraine’s defense,” said William B. Taylor Jr., the acting head of the U.S. Embassy in Kyiv. So Mr. Taylor was appalled when the aid was suspended in July, and even more so when he learned it had been linked to a demand by Mr. Trump for political investigations, including of Joe Biden. “To withhold that assistance for no good reason other than help with a political campaign made no sense,” he said. “It was counterproductive to all of what we had been trying to do. It was illogical. It could not be explained. It was crazy.”

George Kent, the State Department official in charge of Ukraine policy, said in pursuing U.S. anti-corruption initiatives, he had “a front seat to problematic activities by successive prosecutors general in Ukraine.” So he was shocked when he became aware of an effort by Mr. Trump’s personal lawyer, Rudolph W. Giuliani, to smear the U.S. ambassador in Ukraine. “The chief agitators on the Ukrainian side of this effort,” Mr. Kent testified, “were some of those same corrupt former prosecutors I had encountered. . . . They were now peddling false information in order to exact revenge against those who had exposed their misconduct.”

That is the heart of the case against Mr. Trump: that he allied his administration with some of Ukraine’s most corrupt elements, and undercut its military defense at a time when its soldiers were fighting and dying, to obtain what he thought might be evidence of wrongdoing by Mr. Biden or proof that Ukraine rather than Russia was responsible for meddling in the 2016 presidential election. At the least, he wanted to create the impression that such evidence might exist: Mr. Taylor testified about “the odd push” to force Ukrainian President Volodymyr Zelensky to publicly commit to investigating the allegations — an announcement that might hurt Mr. Biden and help Mr. Trump even if nothing came of it.

As expected, Intelligence Committee Republicans devoted some of their time to trying to make the allegations about Mr. Biden and the Ukrainians look credible. To his credit, Mr. Kent, a 27-year veteran of the Foreign Service, responded pithily. Asked if there was any basis for the theory that Ukraine interfered in the election, he responded: “No factual basis.” Asked if there was evidence of wrongdoing by Mr. Biden, he said: “None whatsoever.”

The two witnesses were convincingly nonpartisan. Mr. Kent readily detailed how he had raised concerns about Hunter Biden’s acceptance of a board position on a Ukrainian gas company whose owner had been credibly accused of corruption. Republican attempts to connect that corruption to the Bidens were flimsy: The activities that raised U.S. concerns occurred before Hunter Biden joined the board, and Joe Biden pressed for the removal of a prosecutor who had failed to investigate them. Mr. Trump, meanwhile, demanded not the investigation of the company or its owner, but of the Bidens.

Perhaps the most cynical argument made by Republicans was that neither Mr. Taylor nor Mr. Kent had direct knowledge of Mr. Trump’s demand for a quid pro quo, as neither had spoken to him personally or heard his phone call with Mr. Zelensky. Yet GOP legislators know that senior officials who could testify to Mr. Trump’s actions and motives, including acting chief of staff Mick Mulvaney and former national security adviser John Bolton, have refused to respond to congressional summons on the White House’s instructions. Firsthand testimony may be heard next week from an ambassador who spoke to Mr. Trump about Ukraine repeatedly. But Republicans who genuinely want more direct evidence should be pressing Mr. Trump to stop withholding it.

Read more: