As she runs for her fifth full term, Feinstein is facing a challenge from the left as some liberals question whether the long-serving senator is too moderate for California.
In a tweet, Trump referred to the the top Democrat on the Senate Judiciary Committee as "sneaky" and stated her release of the more than 300-pages of interviews between Glenn Simpson and Judiciary Committee lawmakers and attorneys was "possibly illegal".
Republicans have argued that the tangled history of Fusion GPS's research - it was first backed by anti-Trump Republicans and then by Democrats during the 2016 race - raised doubts about the credibility of investigations into whether any of Trump's aides assisted Russia's efforts to meddle in the election.
Fusion GPS was originally hired to do research during the 2016 Republican primary campaign for a still unknown Republican donor who wanted to defeat Trump.
President Trump slammed Sen. He refused to release transcripts of a key witness's testimony and, last week, Grassley and Sen. "The only way to set the record straight is to make the transcript public".
The lengthy transcript was released over the objections of Republicans, who have been sharply critical of Simpson's firm, Fusion GPS. Republican Sens. Charles E. Grassley (Iowa), committee chair, and Lindsey O. Graham (S.C.), also on the committee with Feinstein, have referred Simpson for criminal prosecution. But Grassley said Wednesday that he has a long history of oversight of the Federal Bureau of Investigation and this was part of it. "Her action undermines the integrity of the committee's oversight work and jeopardizes its ability to secure candid voluntary testimony", such as from Jared Kushner, Trump's son-in-law.
Steele briefed an Federal Bureau of Investigation agent in July 2016. As The Hill explains, a challenging primary is unlikely as California's primary system rewards the highest two finishers, no matter party affiliation, and Feinstein's only notable challenger at this level is a Democrat.
The FBI believed Steele's "information might be credible because they had other intelligence that indicated the same thing, and one of those pieces of information was a human source inside the Trump organization", Simpson testified. The diplomat later reported the conversation to the Federal Bureau of Investigation. In addition to looking into whether members of the Trump campaign colluded with Russian Federation to tilt the election in his favor. special counsel Robert Mueller is also examining whether Trump sought to obstruct justice when he fired Federal Bureau of Investigation director James Comey last May.