We think we can help the South Carolina Republican. Evidently he has not followed closely the depositions and documents collected by three House committees from present and former senior administration officials. If he had, he would see they contain clear proof that Mr. Trump, acting directly and through his lawyer Rudolph W. Giuliani, repeatedly demanded a pledge from Mr. Zelensky to open those political investigations to obtain an Oval Office invitation. There is evidence that U.S. military aid was dependent on the probes, as well.

The chain of evidence begins with the testimony of two State Department officials about a May 23 meeting they had with Mr. Trump to discuss the newly formed government of Mr. Zelensky. Kurt Volker, the administration’s special envoy to Ukraine, and Gordon Sondland, the U.S. ambassador to the European Union, said that the president rejected their appeal to invite Mr. Zelensky to the White House. Instead, said Mr. Volker, Mr. Trump complained that Ukraine was a “corrupt country” that “tried to take me down.”

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According to Mr. Sondland, he “directed those of us present . . . to talk to Mr. Giuliani . . . about his concerns.” Added the ambassador: “It was apparent to all of us that the key to changing the president’s mind on Ukraine was Mr. Giuliani.”

On July 19, Mr. Volker had breakfast with Mr. Giuliani. “He mentioned both the accusations about Vice President Biden and about interference in the 2016 election,” Mr. Volker told Congress, adding that Mr. Giuliani “stressed that all he wanted to see was for Ukraine to investigate what happened in the past.”

Mr. Volker then worked with a top aide to Mr. Zelensky, Andrey Yermak, to set up the July 25 phone call. The morning it took place, Mr. Volker texted Mr. Yermak to clearly lay out the quid pro quo: “Heard from White House-assuming President Z convinces trump he will investigate/‘get to the bottom of what happened’ in 2016, we will nail down date for visit to Washington. Good luck!” During the call, Mr. Trump requested investigations both of the DNC hack and of Mr. Biden; Mr. Zelensky promised to comply; and Mr. Trump seemed to offer a visit to Washington.

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Only it turned out the president and his lawyer were not yet satisfied. Around Aug. 7, according to Mr. Volker, Mr. Giuliani called him and Mr. Sondland. When the two ambassadors raised Mr. Zelensky’s pending White House visit, “Mayor Giuliani then said he believed the Ukrainian president needed to make a statement about fighting corruption, and that he had discussed it with Mr. Yermak,” Mr. Volker testified. The Ukrainians duly produced a draft statement that was “generic” about corruption, Mr. Volker said — only to have it rejected by Mr. Giuliani, who said that “the statement should include specific reference to ‘Burisma’ and ‘2016.’ ” Burisma was the gas company that Mr. Biden’s son Hunter was associated with.

Mr. Volker said he “edited the draft statement by Mr. Yermak to include these points.” On Aug. 10, he received a text from Mr. Yermak saying: “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.” Again, the trade-off of a White House meeting for a promise to investigate the Bidens and the DNC was explicit.

William B. Taylor Jr., the U.S. chargé d’affaires in Kyiv, also knew about the demand for a public statement. On Tuesday, he testified that Mr. Sondland had told him he had heard about the requirement directly from Mr. Trump. Mr. Taylor also said Mr. Sondland had told him he had been wrong to tell the Ukrainians that only a White House meeting was linked to the statement; in fact, “ ‘everything’ was dependent on such an announcement, including security assistance,” Mr. Taylor said. That’s consistent with the news conference last week by White House acting chief of staff Mick Mulvaney, who confirmed that the military aid was held up to leverage a Ukrainian investigation — before issuing an unconvincing retraction.

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The pressure campaign continued into September. On Sept. 8, Mr. Taylor said, Mr. Sondland informed him that after talking to Mr. Trump, he had told Mr. Zelensky that if he “did not ‘clear things up’ in public, we would be at a ‘stalemate.’ ” Added Mr. Taylor: “I understood a ‘stalemate’ to mean that Ukraine would not receive the much-needed military assistance.”

The Ukrainians eventually told Mr. Volker that they did not want to promise investigations of Mr. Biden and the Democrats. The statement, Mr. Volker said, “was shelved.” And Mr. Zelensky never got his White House meeting. U.S. military aid, which Mr. Trump had ordered held up on July 18, was released on Sept. 11 — only after the corrupt quid pro quo was becoming public. By that date, House Democrats had announced that they would investigate whether the aid had been blocked to force Ukraine to assist Mr. Trump’s reelection campaign.

Mr. Graham and some other Republicans would portray the July 25 phone call as an isolated event in which Mr. Trump did not clearly conclude a quid pro quo with Mr. Zelensky. But the evidence presented to Congress shows that the call was part of a process that extended over three months and included repeated and specific demands for Ukraine to undertake political investigations, including of Mr. Trump’s possible 2020 opponent, lodged by Mr. Trump and by the lawyer he told top aides to work with on the deal.

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Mr. Graham is himself a lawyer and former military prosecutor. He surely can recognize this corrupt campaign for what it is. The question is whether he, and other Republicans, have the moral courage to do so.