Washington — Back in July 2016, just before the formal launch of the FBI’s investigation of Russian meddling in the U.S. presidential election, a bureau informant met in Britain with a Trump campaign adviser and energy consultant named Carter Page who had just returned from a trip to Moscow.

Page’s encounter with the FBI informant is ground zero of what President Trump has claimed was a “Spygate” plot to implant a mole in his campaign. Trump’s conspiratorial thesis is challenged by some prominent Republican officials (including House Speaker Paul Ryan), as well as by court records, interviews and other materials.

The sharpest rebuttal to Trump came from Rep. Trey Gowdy, the Republican chairman of the House Oversight Committee. He told Fox News that after talking with intelligence officials about the probe, “I am even more convinced that the FBI did exactly what my fellow citizens would want them to do.”

Page disputes that. He tweeted that Gowdy’s comments were a “fitting … sequel” to the chairman’s report that largely exonerated Hillary Clinton in the Benghazi affair, and described Gowdy’s actions as “wasting big $’s, self-promoting PR stunts.”

Page hasn’t been accused of any wrongdoing, and he has provided documents and testimony to congressional investigators. Page told The Washington Post last year that he’d had “extensive discussions” with the FBI. Asked if he was cooperating with special counsel Robert Mueller’s inquiry, Page told me in an email that “the special counsel [has] been less inclined so I have nothing special to report.”

Given the uproar, it’s useful to examine the background of the Page story. The biggest lesson I can find amid the contradictory statements is that the Kremlin can be very aggressive indeed in trying to cultivate Americans. This counterintelligence primer never seems to have been offered to members of the Trump campaign.

What had Page been doing in Moscow before he met the FBI informant? In a July 8, 2016, email to campaign colleagues he said that along with making a speech, he’d had a “private conversation” with Russian Deputy Prime Minister Arkady Dvorkovich and received “incredible insights and outreach” from senior Russian officials.

So how did this part-time academic and energy consultant find himself at the center of a web of intrigue? The answer is partly that, like so many others in the Trump-Russia saga, Page started off as a bit player — a former banker trying to parlay his contacts into useful connections.

Page’s Russia experience began in 2004, when he joined the Moscow office of Merrill Lynch, dealing with Gazprom, the government-controlled gas company. Sergey Aleksashenko, who supervised Page as CEO of Merrill Lynch Russia, explains: “Carter was fairly good, no complaint. But he was not creative.” Aleksashenko says Page left Moscow in 2007 when told he wouldn’t be promoted above vice president there; Page says that account is “false” and that Aleksashenko, now a fellow at the Brookings Institution, has been critical of Trump supporters.

Back in New York, Page in 2008 launched a consulting firm called Global Energy Capital. Sergei Yatsenko, a former senior investment officer at Gazprom, joined him as a partner in 2010. Energy industry sources say the firm helped a Gazprom subsidiary do a small gas project in Iraqi Kurdistan in 2012 and a few other deals. (Yatsenko declined through an intermediary to discuss his relationship with Page.)

In 2013, Russian intelligence allegedly made a run at Page. The story is outlined in the 2015 indictment of three Russian intelligence officers, which includes a transcript of FBI surveillance of Victor Podobnyy, a member of the Russian U.N. team who was actually an intelligence officer, talking about a target identified as “Male-1,” who was Page. (Page confirmed last year that he was “Male-1” and blasted the “illegal leaking of my identity.”)

Podobnyy had some tart comments about Page’s gullibility: “I think he is an idiot and forgot who I am [at the Russian mission]. … He got hooked on Gazprom thinking that if they have a project, he could rise up,” the Russian spy told his colleagues, according to the FBI transcript. He said his plan was to “feed him [Page] empty promises” and “get documents from him.”

Page confirmed to the House Intelligence Committee last November that he exchanged emails with the Russians and talked about Gazprom and shale-gas projects; he said this energy information was similar to what he told his students.

Mueller will surely untangle the Page narrative and all the other threads of the Russia investigation. One simple takeaway: When that nice Russian asks you for a favor, think twice.

— David Ignatius is a columnist for Washington Post Writers Group.