The head of the research firm behind a dossier of allegations against then-presidential candidate Donald Trump told congressional investigators that someone inside Trump’s network had also provided the FBI with information during the 2016 campaign, according to a newly released transcript, a claim quickly disputed by people close to the investigation into Russian interference in the election.

Glenn R. Simpson, a founder of the research firm Fusion GPS, spoke to investigators with the Senate Judiciary Committee for 10 hours in August. As the partisan fight over Russian interference in the 2016 election has intensified, Simpson has urged that his testimony be released, and a copy of the transcript was made public Tuesday.

It was released by the ranking Democrat on the Senate Judiciary Committee, Sen. Dianne Feinstein of California. That decision marks the most serious break yet in the cooperative relationship she has had with the Republican chairman of the committee, Sen. Charles E. Grassley (R-Iowa).

A spokesman for Grassley called Feinstein’s move “totally confounding” and done without consultation. “Her action undermines the integrity of the committee’s oversight work and jeopardizes its ability to secure candid voluntary testimony relating to the independent recollection of future witnesses,’’ said the spokesman, Taylor Foy.

Feinstein said she released the transcript to set the record straight. “The innuendo and misinformation circulating about the transcript are part of a deeply troubling effort to undermine the investigation into potential collusion and obstruction of justice,’’ she said.

A representative for Fusion GPS did not immediately offer a comment.

Fusion GPS was hired in mid-2016 by a lawyer for Hillary Clinton’s presidential campaign and the Democratic National Committee to dig into Trump’s background. Earlier that year, the firm had been probing Trump for a conservative website funded by a GOP donor, but that client stopped paying for the work after it became clear Trump would win the GOP nomination, according to people familiar with the matter.

After Democrats began paying for the research, Fusion GPS hired Christopher Steele, a former senior officer with Britain’s intelligence service, MI6, to gather intelligence about any ties between the Kremlin and Trump and his associates. Steele’s reports were eventually compiled into a dossier alleging the Trump campaign coordinated with the Kremlin — a claim the president has repeatedly denied.

Steele first reached out to the FBI with his concerns in early July 2016, according to people familiar with the matter. When they re-interviewed him in early October, agents made it clear, according to Simpson’s testimony released Tuesday, that they believed some of what Steele had told them.

“My understanding was that they believed Chris at this point — that they believed Chris 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,” Simpson said.

Read the full story at The Washington Post.

Glenn R. Simpson, former Wall Street Journal journalist and a founder of the research firm Fusion GPS, arrives to appear before a closed House Intelligence Committee hearing in November. (Pablo Martinez Monsivais/AP)

Glenn R. Simpson, former Wall Street Journal journalist and a founder of the research firm Fusion GPS, arrives to appear before a closed House Intelligence Committee hearing in November. (Pablo Martinez Monsivais/AP)