Is it wrong to lie to the FBI to feed your family? Well, what if your family don’t like bread, they like email hacks that will bring down Crooked Hillary?

During a night of heavy drinking at an upscale London bar in May 2016, George Papadopoulos, a young foreign policy adviser to the Trump campaign, made a startling revelation to Australia’s top diplomat in Britain: Russia had political dirt on Hillary Clinton.

About three weeks earlier, Mr. Papadopoulos had been told that Moscow had thousands of emails that would embarrass Mrs. Clinton, apparently stolen in an effort to try to damage her campaign.

Exactly how much Mr. Papadopoulos said that night at the Kensington Wine Rooms with the Australian, Alexander Downer, is unclear. But two months later, when leaked Democratic emails began appearing online, Australian officials passed the information about Mr. Papadopoulos to their American counterparts [what an unusual idea! –ed.], according to four current and former American and foreign officials with direct knowledge of the Australians’ role.

The hacking and the revelation that a member of the Trump campaign may have had inside information about it were driving factors that led the F.B.I. to open an investigation in July 2016 into Russia’s attempts to disrupt the election and whether any of President Trump’s associates conspired.

If Mr. Papadopoulos, who pleaded guilty to lying to the F.B.I. and is now a cooperating witness, was the improbable match that set off a blaze that has consumed the first year of the Trump administration, his saga is also a tale of the Trump campaign in miniature. He was brash, boastful and underqualified, yet he exceeded expectations. And, like the campaign itself, he proved to be a tantalizing target for a Russian influence operation.