Here are some highlights from the transcript released Tuesday of Glenn Simpson's testimony to the Senate Judiciary Committee.
"The transcript of Glenn Simpson's lengthy responses to the Senate Judiciary Committee's questioning speaks for itself", Fusion GPS said. The firm commissioned the dossier, which was initially paid for by a conservative website and then later by Democrats, including Hillary Clinton's presidential campaign.
The Washington research firm has been under attack by the White House and Republican lawmakers over the dossier, which is central to investigations in Congress and by a federal special counsel into allegations that Russian Federation interfered in the election to help Trump win, and any potential collusion by the Trump campaign.
Feinstein's decision came after a tense back-and-forth between Republicans and Democrats over what to do with the transcript of Simpson's interview, which he provided on August 22.
In a statement, Feinstein said that she released Simpson's testimony after conferring with her fellow committee Democrats.
He also testified that the Federal Bureau of Investigation told Steele it had someone inside the Trump network who could corroborate Steele's claims.
"Essentially what he told me was they had other intelligence about this matter from an internal Trump campaign source", Simpson said.
"The only way to set the record straight is to make the transcript public", she said in a statement.
Mr Simpson declined to say who he suspected the whistle-blower to be, but did not think it was a source of Mr Steele's. The New York Times reported last month that Papadopoulos told the diplomat that Russian Federation had thousands of emails that would embarrass Clinton and that the Australians' subsequent tip to the FBI about the conversation helped persuade the bureau to investigate potential coordination between Russian Federation and the Trump campaign.
Christopher Steele told the political research firm that hired him, Fusion GPS, that what he uncovered from Russian sources was serious enough to bring to the attention of US law enforcement authorities, according to a transcript released on Tuesday.
Other Republicans on the panel were less concerned.
A spokesman for Grassley, Taylor Foy, called it "confounding" that Feinstein released the transcript "unilaterally", over the objections of the Republican majority. That decision marks the most serious break yet in the cooperative relationship she has had with the Republican chairman of the committee, Sen.
"This was like, you know, you're driving to work and you see something happen and you call 911", Simpson told investigators. Chuck Grassley, issued a criminal referral last week for Steele, alleging the committee had reason to believe that the former spy had lied to authorities about his conversations with the press regarding the dossier.
He also disputed Republican charges that his firm is linked to Democrats, saying the firm takes clients from both sides of the aisle.
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