SECRETARY OF State Mike Pompeo claims to be defending the “dedicated professionals” at the State Department and the policy they have pursued in Ukraine. The truth is pretty much the opposite. Mr. Pompeo stood by while President Trump and his personal lawyer twisted Ukraine policy to their own ends, and he enabled their vicious attack on the State Department’s ambassador in Kiev. Now he is trying to obstruct her and other professionals from telling their stories to Congress.

Mr. Pompeo made two accurate statements at a news conference in Rome on Wednesday. Ending days of dissembling, he confirmed that he was a participant in the July 25 phone call during which Mr. Trump pushed Ukraine’s president to undertake political investigations, including of Joe Biden. And Mr. Pompeo said, accurately, that U.S. policy toward Ukraine has been “consistent” for some time in seeking to counter “the threat that Russia poses” to the country and in helping the Ukrainians get “graft . . . and corruption [out] of their government.”

What the secretary of state did not acknowledge is that he allowed Mr. Trump and lawyer Rudolph W. Giuliani to trash that policy. Mr. Pompeo did nothing to stop Mr. Giuliani from allying himself with some of Ukraine’s most corrupt figures to peddle false stories about Mr. Biden, as well as conspiracy theories about Ukraine’s role in the 2016 presidential election. One of those tales — that the hacking of the Democratic National Committee was done not by Russia but by Ukrainians — is a classic piece of disinformation that serves Vladi­mir Putin’s campaign to undermine Ukraine’s pro-Western government.

Mr. Pompeo listened on July 25 while Mr. Trump pressed Ukrainian President Volodymyr Zelensky to investigate that theory as well as the false story that Mr. Biden sought the removal of a Ukrainian prosecutor to protect his son. He listened while Mr. Trump slandered the former U.S. ambassador to Ukraine, Marie Yovanovitch — a dedicated Foreign Service professional — whose tour in Kiev Mr. Pompeo had cut short.

Ms. Yovanovitch boldly campaigned against Ukrainian government corruption. Her reward was a humiliating recall and a promise by Mr. Trump that “she is going to go through some things.” Meanwhile, according to the rough transcript released by the White House, Mr. Trump never mentioned “graft” or “corruption” to Mr. Zelensky, much less “the threat that Russia poses.” Mr. Pompeo’s claim that the conversation was “in the context” of long-standing U.S. policy is demonstrably false.

So, too, was Mr. Pompeo’s assertion that a request by House committees for depositions from Ms. Yovanovitch and other State Department officials was improper. Mr. Pompeo claimed the committees had not followed proper procedure or given the officials enough time to prepare. He insisted that State Department lawyers must be present at all depositions to prevent the disclosure of “privileged information.” The House committee chairmen correctly interpreted this bluster: Mr. Pompeo, they said, was “intimidating Department witnesses in order to protect himself and the President.”

Fortunately, one of those witnesses, former special envoy to Ukraine Kurt D. Volker, is due to testify on Thursday, and Ms. Yovanovitch has reportedly been scheduled for next week. They and other State Department professionals should not hesitate to tell Congress the truth about how Mr. Pompeo enabled the destruction of U.S. diplomacy.

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