NYT [...] The woman had set up the meeting to discuss foreign policy issues. But she was actually a government investigator posing as a research assistant, according to people familiar with the operation. The F.B.I. sent her to London as part of the counterintelligence inquiry opened that summer to better understand the Trump campaign’s links to Russia.

The American government’s affiliation with the woman, who said her name was Azra Turk, is one previously unreported detail of an operation that has become a political flash point in the face of accusations by President Trump and his allies that American law enforcement and intelligence officials spied on his campaign to undermine his electoral chances. Last year, he called it "Spygate."

Ms. Turk went to London to help oversee the politically sensitive operation, working alongside a longtime informant, the Cambridge professor Stefan A. Halper. The move was a sign that the bureau wanted in place a trained investigator for a layer of oversight, as well as someone who could gather information for or serve as a credible witness in any potential prosecution that emerged from the case.

A spokesman for the F.B.I. declined to comment, as did a lawyer for Mr. Halper, Robert D. Luskin. Last year, Bill Priestap, then the bureau’s top counterintelligence agent who was deeply involved in the Russia inquiry, told Congress during a closed-door hearing that there was no F.B.I. conspiracy against Mr. Trump or his campaign.