Top members of the Senate Judiciary Committee are signaling they are heading in separate directions on the panel's probe on the 2016 presidential election, potentially threatening what had been a bipartisan investigation.

Sen. Dianne Feinstein Dianne Emiel FeinsteinBiden leads Trump by 12 points among Catholic voters: poll Names to watch as Trump picks Ginsburg replacement on Supreme Court McConnell says Trump nominee to replace Ginsburg will get Senate vote MORE (D-Calif.) said on Thursday that she was "disappointed" by the split, which appears to be spawning out of a GOP push to revisit Obama-era scandals.

"All I'm saying is that we have decided that each side is going to take a course and we'll share and if the other side wants to participate they can. That's all I'm going to say. So we are going ahead with some things," Feinstein told reporters.

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She added the focus for Democrats would be "obstruction of justice and whether there was cooperation-collusion between the Trump administration and Russia."

Asked about if there was a split, Sen. Chuck Grassley Charles (Chuck) Ernest GrassleyGardner signals support for taking up Supreme Court nominee this year Grassley, Ernst pledge to 'evaluate' Trump's Supreme Court nominee McConnell digs in on vow to fill Ginsburg's Supreme Court seat MORE (R-Iowa), chairman of the Judiciary Committee, said the question was "misinformed" but appeared to acknowledge they wouldn't always be working in tandem on every issue.

"Because I'm doing what I do, she wants to do what she wants to do, and then we're doing a lot of things together. So if your question implies a lack of cooperation that's entirely the wrong place to start," he told reporters.

Asked for examples of where he thought Republicans would need to go it alone, Grassley pointed to a recent spate of letters and the Uranium One deal.

"I suppose the most recent example would be my asking for special counsel. ... We run into this Uranium One investigations and that involves another administration that she may not want to go into," he said.

Feinstein, who is facing a primary challenge in 2018 from the left, has faced pushback from liberals for her work on the Judiciary Committee and being too collegial with Republicans.

Grassley called for a special counsel after The Hill reported that the FBI had been leading a criminal investigation into allegations that the Russians used racketeering and other corrupt schemes to influence the American nuclear industry during the time the uranium deal was in the process of being approved.

He added on Thursday that he still believes the committee's collusion investigation is bipartisan "based upon the proposition that now what we're doing on Uranium One makes it very bipartisan."

The Judiciary Committee is one of two panels in the Senate probing Russia's election interference and potential ties between the Trump campaign and Moscow. It's also looking into the firing of former FBI Director James Comey and potential political interference by the Justice Department into FBI investigations.

The Intelligence Committee, which Feinstein is also a member of, is also looking into the 2016 election.

Grassley sent out roughly a dozen letters, without Feinstein's signature, earlier this month, including ones to Loretta Lynch, Attorney General Jeff Sessions Jefferson (Jeff) Beauregard SessionsGOP set to release controversial Biden report Trump's policies on refugees are as simple as ABCs Ocasio-Cortez, Velázquez call for convention to decide Puerto Rico status MORE and Trump's son-in-law Jared Kushner.

A spokesman for Grassley told Mother Jones that the letters were sent without Feinstein to avoid a delay. Feinstein, however, said she didn't find out about the letters until after the fact.

Grassley added on Thursday that regardless of whether Feinstein sends a letter or he sends a letter, "both sides [of] staff can be involved in the q-and-a."

The panel's investigation into Russia's election interference has been slow going, with lawmakers sporadically airing frustration that they feel they are playing second fiddle to the Senate Intelligence Committee's probe.

Sen. Richard Blumenthal (D-Conn.) is urging the panel to focus on potential collusion between Russia and the Trump campaign.

"The president has done everything he can — calling the investigation a hoax, bringing distracting issues to deflect attention from the potential obstruction of justice by his administration and possibly by himself into the investigation on Russian meddling, and Trump's alleged collusion with that meddling," Blumenthal told CNN.

Sen. Lindsey Graham Lindsey Olin GrahamGraham: GOP will confirm Trump's Supreme Court nominee before the election Fox's Napolitano: Supreme Court confirmation hearings will be 'World War III of political battles' Grassley, Ernst pledge to 'evaluate' Trump's Supreme Court nominee MORE (R-S.C.) acknowledged that there appeared to be a split between Grassley and Feinstein, but argued the panel's wide-ranging investigation should be bipartisan.

"That'd be a shame. Because it's now the common view that we need to investigate all things Russia and Trump. We have the same view about all things GPS Fusion and Clinton," Graham said, referring to the firm linked to a controversial research dossier on Trump.

He added that the committee should be unified on exploring anything related to Russia, and he expected a hearing later this month with social media companies.

"We just go where the facts take you. ... I am willing to do subpoenas in the Trump world. They need to be willing to do subpoenas in the Democratic world," he said.