Then suddenly, as quick as the headlines went up, some one close to Fusion was waving off reporters. Mr. Simpsonhad "mischaracterized" the source. It was not some one on the Trump inside, but apparently an Australian diplomat

He was featured in a Dec. 30 New York Times story as the source who tipped off the FBI. Campaign volunteer George Papadopoulos told him over drinks that a Russian-linked professor knew of "thousands" of Hillary Clinton emails in the hands of Moscow.

How Mr. Simpson knew of the diplomat last August was unclear. He would have known of him in January when he wrote an op-ed in the New York Times in which he again told of an insider source.

"As we told the Senate Judiciary Committee in August, our sources said the dossier was taken so seriously because it corroborated reports the bureau had received from other sources, including one inside the Trump camp," he wrote.

Moments after Sen. Dianne Feinstein, California Democrat, unilaterally released the transcript, the inside-source story spread, especially in London. The city is home base of Christopher Steele, the ex-British spy who wrote the dossier.

In his testimony, Mr. Simpson told of Mr. Steele's meeting with FBI agents in Rome in September 2016. Mr. Steele told Mother Jones magazine he was trying to jump-start an investigation into President Trump.

Mr. Simpson testified, "Essentially what he told me was they had other intelligence about this matter from an internal Trump campaign source and that ‐ that they ‐ my understanding was that they believed Chris at this point ‐ that they believed Chris's information might be credible because they had other intelligence that indicated the same thing and one of those pieces of intelligence was a human source from inside the Trump organization."