Additionally, Weldon appears to have knowledge of a key instance in which a foreign national sought to influence the president through one of his closest advisers—a central theme of Special Counsel Robert Mueller’s ongoing investigation into Russia’s election interference.

At issue is the question of whether the president and his associates have sought to trade favors with foreign entities for personal gain. Mueller has been investigating, for example, whether Paul Manafort, Trump’s former campaign chairman, tried to use his position to repay old debts to a Russian oligarch, and whether Ivanka Trump and her husband, Jared Kushner, have influenced Trump’s foreign-policy decisions based on their business interests. Mueller is also investigating foreign-linked donors to Trump’s inauguration fund.

Asked how Weldon was connected to the campaign, Feinstein’s office would not elaborate, citing the sensitivity of the Judiciary Committee’s ongoing investigation. Weldon declined multiple interview requests. But a letter Feinstein sent last year to Trump’s longtime personal attorney, Michael Cohen, may provide a clue. In it, Feinstein asked for all of Cohen’s communications “to, from, or copied to” Weldon, as well as correspondence “related to” Weldon, along with nearly two dozen other people.

Weldon’s name stuck out—he had served as a member of Congress and had not been mentioned previously in relation to the Russia investigation. But his connection to Cohen may lie in a mutual acquaintance who has since testified before Mueller’s grand jury: a former member of the Ukrainian Parliament named Andrii Artemenko.

In January 2017, shortly after Trump’s inauguration, Artemenko met with Cohen at a New York City hotel to discuss bringing peace to Russia and Ukraine. Also present was Felix Sater, a friend of Cohen’s and a former business partner of Trump’s. All three men confirmed to me that this meeting took place. When Artemenko pitched the peace plan, which involved lifting sanctions on Russia in exchange for Russia’s retreat from eastern Ukraine, Cohen said he would deliver it to then–National-Security adviser Michael Flynn, according to The New York Times. Artemenko told the newspaper that he had received encouragement for his peace plan from top aides to Russian President Vladimir Putin. Artemenko also told me that he had gotten “confirmation” that the peace plan had been left on Flynn’s desk. But Cohen walked back his story after the meeting was exposed by the Times, insisting that he had thrown the plan in the garbage. (Flynn has not responded to multiple requests for comment.)

Weldon, who has known Artemenko, the Ukrainian politician, for more than a decade, was furious that The New York Times had learned about the meeting, according to a person who spoke with him at a separate gathering last March, two weeks after the story in the Times had been published. “We were so close,” Weldon complained, this source recalled. Then Weldon dropped a bombshell: “He said [he and Artemenko] had already secured funding for the promotion of the plan from Viktor Vekselberg’s fund in New York City.”