The top Republican and Democrat on the House Intelligence Committee hurled salvos at each other on Wednesday, raising partisan tensions over the investigation into Russian meddling in the U.S. election.

In a tweet, the California Democrat questioned what the "holdup" was after the White House denied reports Tuesday that it tried to stop Yates from testifying.

Also Wednesday, Nunes told NBC News that "it appears like the Democrats aren't really serious" about the probe. The California Republican said "we're going to do an investigation with our without" Democrats.

Their statements escalated the fight over the probe into whether Russian hacking was done in collusion with Donald Trump 's campaign to help him win the 2016 presidential election. Some Democrats have accused Nunes of trying to undermine the investigation's independence from the White House and called on him to recuse himself from it.

Nunes has said he sees no reason to step aside from the investigation, and House Speaker Paul Ryan has expressed confidence in him. Still, it remains to be seen how the investigation will proceed.

On Friday, Nunes canceled the public hearing that had been set for Tuesday with testimony from fired acting Attorney General Sally Yates, ex-CIA Director John Brennan and former Director of National Intelligence James Clapper. Nunes and White House Press Secretary Sean Spicer denied that the White House had any influence on the decision to cancel the hearing.

Yates warned the White House in January that former National Security Advisor Michael Flynn could be vulnerable to blackmail after he made incorrect statements about his contacts with Sergey Kislyak, the Russian ambassador to the U.S. The next month, Flynn was forced to resign for what the White House said were his contradictory statements to Vice President Mike Pence .

Trump subsequently fired Yates after she told Justice Department lawyers not to defend his first executive order restricting travel from seven Muslim-majority countries.

Schiff on Monday called for Nunes to recuse himself from "any investigation" into the president's campaign and transition team. Nunes served on the Trump transition team. The California Republican admitted that he met with an unidentified source on the White House grounds to review intelligence reports ahead of his claim that Trump transition members' communications were "incidentally" swept up by U.S. intelligence officials.

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