THE ROUGH transcript of President Trump’s July 25 phone call with Ukrainian President Volodymyr Zelensky prompted a debate about whether, in pressing for politicized investigations of alleged Ukrainian interference in the 2016 election and of Joe Biden, Mr. Trump dangled rewards for Mr. Zelensky as a quid pro quo. In our view, the transcript contained at least a hint that Mr. Trump was linking the “favor” he wanted to arms sales, and clear evidence that he was tying it to a White House invitation.

That conclusion is now confirmed. Text messages among U.S. diplomats and a Ukrainian official released by House committees definitively show that not only did the Trump administration seek to extract Ukrainian promises of political probes in exchange for a summit meeting, but also they spent weeks negotiating the deal both before and after the Trump-Zelensky phone call.

There was no lack of clarity on either side. “Heard from the White House,” U.S. special envoy to Ukraine Kurt Volker texted a top aide to Mr. Zelensky on July 25, just ahead of the call. “Assuming President Z convinces trump he will investigate/ ‘get to the bottom of what happened’ in 2016, we will nail down date for a visit to Washington.”

About two weeks later, amid negotiations over what, exactly, Mr. Zelensky would say in publicly announcing the probes, the aide, Andrey Yermak, texted Mr. Volker: “I think it’s possible to make this declaration and mention all these things. . . . But it will be logic to do after we receive a confirmation of date.”

In the end, the deal did not go through. Instead, the record shows that Mr. Trump and his retainers kept raising their demands, like a casino developer squeezing a plumbing contractor.

Mr. Zelensky was supposed to get his meeting date after promising the investigations in the July 25 phone call. Instead, the Ukrainians were told Mr. Zelensky needed to make a public statement committing to the probes. Mr. Volker told Congress Thursday that when the Ukrainians then offered a general statement about fighting corruption, it was rejected by Mr. Trump’s personal lawyer, Rudolph W. Giuliani, who said Mr. Zelensky had to refer specifically to allegations of Ukrainian interference in the 2016 election and to the gas company that employed Mr. Biden’s son Hunter. In the end, the Ukrainians — to their credit — refused.

Meanwhile, the senior U.S. diplomat in Kiev, William B. “Bill” Taylor, had become concerned that not just a White House meeting but also U.S. military aid to Ukraine — which Mr. Trump had suspended — were linked to the demand for investigations. In an enigmatic text message on Sept. 8, Mr. Taylor referred to a “nightmare” scenario in which “they give the interview and don’t get the security assistance.” That sounds like a reference to yet another political trade-off, this time involving the $391 million in aid Mr. Trump was sitting on. The next day, the career diplomat texted: “I think it’s crazy to withhold security assistance for help with a political campaign.”

Congress clearly has more to learn here, from Mr. Taylor and others. As we have written, our information is that the White House was conditioning security assistance on Ukraine’s promise to conduct the politically motivated investigations. But legislators already know this much: Mr. Trump literally used his office — in the form of a promised White House meeting — to induce a foreign leader to investigate a potential opponent in the 2020 election. That was a blatant act of corruption.

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