WASHINGTON — The once-bipartisan Senate Judiciary Committee investigation into Russian influence in the 2016 election has broken along partisan lines, with the committee’s top Democrat contacting witnesses independently and asking for a broad swath of new information.

After months of negotiations with Senate Judiciary Chairman Chuck Grassley stalled, California Sen. Dianne Feinstein sent five letters of her own on Friday to witnesses and companies involved in the probe. The letters were sent to the White House, Facebook, Twitter and President Donald Trump’s personal lawyer, Michael Cohen. There is also a letter to Cambridge Analytica, a data firm working for Trump’s campaign during the 2016 election.

The inquiries are designed to get more information about whether the Russian meddling was in any way connected with Trump’s campaign. Feinstein indicated this week that negotiations had broken down with Grassley, who has also sought to investigate issues surrounding Democratic presidential candidate Hillary Clinton.

The two senators have been talking since the summer about how to handle several witnesses, including whether to subpoena Trump’s former campaign chairman, Paul Manafort, and whether to call Trump’s son Donald Trump Jr. for a public hearing.

Both men were involved in a June 2016 campaign meeting with Russians. Trump Jr. spoke to committee staff behind closed doors in September.

As a member of the minority party, Feinstein could have a hard time getting responses. But she is trying anyway, asking the social media companies in particular for a wide range of information, some of which they have already declined to turn over because of privacy concerns. Facebook and Twitter, along with Google, will testify before a panel subcommittee on Tuesday about the Russian meddling.

In the White House letter, Feinstein asks White House counsel Don McGahn for a range of documents related to fired FBI Director James Comey. Going beyond a May request for documents she made with Grassley, which was not answered, Feinstein is asking for several other letters and memos surrounding his firing and about other figures key to the panel’s probe.

A release from Feinstein’s office said the letters were the “first tranche” and that “additional requests are expected to be sent in the coming weeks.”

Grassley has been sending his own letters in the Russia probe, including to Russians and people connected to Trump who were in the June 2016 meeting. Unlike letters sent earlier in the year, they were from Grassley alone and not Feinstein.

Feinstein has also been working on legislation with Connecticut Sen. Richard Blumenthal, another Democrat on the committee. The bill hasn’t yet been finalized but would “potentially would make crystal clear that working with America’s enemies to undermine American elections is a crime,” according to Blumenthal.

Blumenthal said Friday that he believes the investigation will continue, and “my hope is that we will all eventually come together.”

Also Friday, the House intelligence committee announced that it will hold a hearing Nov. 2 with Carter Page, a foreign policy adviser to the Trump campaign. The hearing is listed as “open in a closed space,” which a committee spokeswoman said means that it will be closed to press, but a transcript will eventually be released.