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. [Read the full transcript of Glenn Simpson’s Senate testimony] 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.