The ongoing hearing has largely split across partisan lines, with Democrats focusing on issues of Russian interference and Republicans questioning Comey and National Security Agency head Michael S. Rogers about how scary and bad leaks are.
FBI director James Comey on Monday confirmed the existence of an ongoing investigation into whether anyone associated with President Donald Trump coordinated with the Russian government as part of Russia's efforts to interfere with the 2016 U.S. election.
For more than two weeks, Trump has refused to back down on his allegation, even as a string of officials, including House Speaker Paul Ryan and the top Republican and Democratic lawmakers on both the Senate and House Intelligence Committees, have said there is no evidence to support Trump's March 4 wiretapping claims he made in a series of Twitter comments.
Nunes said on "Fox News Sunday" that he was not aware of any warrant that would have allowed such a wiretap.
Yet Nunes also rejected Trump's claim that there was a wiretap of Trump Tower, Trump's NY residence and headquarters for both his business and campaign.
"We've offered no opinion, have no view, have no information on potential impact, cause it's never something that we looked at", Comey said.
The president's political position was already shaky heading into Monday's hearing, the first of several public sessions the House and Senate intelligence committees are expected to hold.
On March 5, the White House called for Congress to investigate-now, lawmakers in both chambers of Congress are demanding the Federal Bureau of Investigation clear up the president's claims.
"What about all of the contact with the Clinton campaign and the Russians?"More news: Warning to motorists as snow and ice forecast
Trump's White House spokesman, Sean Spicer, last week suggested that the wiretapping was carried out by British agents, citing a statement on Fox News by a legal analyst, Andrew Napolitano.
"The real problem here is you had a foreign adversarial power intervene in our election, a very close election, and what our intelligence community tells us is they're going to do it again", Adam Schiff, the senior Democrat on the House intelligence panel, told CBS News Monday. "There's certainly enough for us to conduct an investigation".
Manafort left the campaign in August, when news reports about his business ties to pro-Moscow Ukrainian oligarchs became a political liability. "This story is FAKE NEWS and everyone knows it!"
But Devin Nunes, the Republican who chairs the committee, said Sunday that they have so far has found no evidence that Trump's campaign colluded with Russian Federation.
In follow-up tweets Monday morning, the president claimed Democrats "made up and pushed the Russian story" to explain Democratic nominee Hillary Clinton's loss in the presidential election.
"The possibility of Trump officials conspiring with a foreign adversary to influence a US election represents a grave threat to our national security and our democracy, and the American people deserve answers", the statement reads.
The anti-secrecy group WikiLeaks subsequently released thousands of emails from the files of Clinton campaign chief John Podesta in the month before the election, showing embarrassing, behind-the-scenes efforts of Democratic operatives to help Clinton win the party's presidential nomination.
But the Trump administration has rebuffed any contention that its campaign aides colluded with Russian officials in that cyberattack.