A former Trump campaign aide who took a guilty plea in special counsel Robert Mueller’s Russia probe was the linchpin of the FBI’s investigation of Kremlin influence in the 2016 election, new reports say.

In a drunken gossip session with an Australian diplomat in London in May 2016, Trump aide George Papadopoulos claimed that Russia held political dirt on Hillary Clinton, the New York Times said Saturday.

Months later, hacked emails from the Democratic National Committee showed up on WikiLeaks, and the Australians told the FBI about the Papadopoulos conversation.

The disclosure sparked the FBI’s probe into possible collusion between the Trump campaign and the Kremlin, sources told the Times.

Papadopoulos, 29, pleaded guilty in October to charges of lying to the FBI about contacts he had with Russians during the 2016 campaign. He is now a cooperating witness.

The ambitious aide made many attempts to insinuate himself into Trump’s campaign, which lacked the experienced political hands typical of presidential electoral efforts, the report says.

His efforts to broker a Trump meeting with Russian President Vladimir Putin were rebuffed. But Papadopoulos succeeded in helping organize a September 2016 visit with Egyptian President Abdel Fattah al-Sisi.

Republicans allege that a shady dossier — financed by the Clinton campaign as a piece of anti-Trump opposition research — was the real impetus for the FBI investigation.

Sen. Lindsey Graham (R-SC) called on Friday for a new special prosecutor to examine whether the Obama administration used the dossier as evidence in a secret federal court hearing.

“What I’ve gathered in the last couple of days bothers me a lot,” Graham told Fox News on Friday. “This cannot be the new normal.”

The Department of Justice used Foreign Intelligence Surveillance Act rules to get a warrant to snoop on Trump associates during the presidential campaign and the post-election transition, say multiple reports.