The hearing, which also features testimony from National Security Agency Director Mike Rogers, could shed light on the state of FBI investigations into the extent of Russian meddling in the election campaign.
The top Democrat on the committee, Rep. Adam Schiff, said it was not yet known whether the Russian operation was aided by USA citizens, "including people associated with the Trump campaign". Department of Justice attorneys must then present that request to a court for approval.
He also disputed allegations that British intelligence services were involved in the wiretapping.
"If there's evidence that leads in that direction, i think there's a case that could be made that we need the tax returns to either corroborate or disprove what the russians might have been doing in terms of trying to financially entangle the Trump Organization", he said. The Trump White House has provided zero evidence that is true. Trump is returning from a trip to his Mar-a-Lago estate in Palm Beach, Fla.
Trump's official Twitter account also tweeted an exchange between the Director of the National Security Agency and committee chair Devin Nunes on how there is no evidence vote totals were changed in a series of 2016 battleground states.
"But it is also possible, maybe more than possible" that it isn't a coincidence, Schiff said.
"The real story the Congress, the Federal Bureau of Investigation and all others should be looking into is the leaking of Classified information", Trump tweeted at 7:02 a.m. Must find leaker now!
Comey and Rogers also stated that there was no evidence that Russian Federation interfered with actual votes during the 2016 election.
"So it's not too far of a logical leap, that the assertion that you have told the Congress that there was no influence on the electoral process, is not quite right", Himes asked. The video clip shows Comey and Rogers confirming they have no evidence indicating that Russian Federation altered vote tallies on Election Day in swing states like Florida, North Carolina and Ohio. And Comey said law enforcement officials were investigating potential links between top Trump campaign figures and the Russian Federation government.
The FBI director refused to "characterize" tweets Trump posted earlier the month alleging Obama wiretapped Trump Tower in New York City past year.
"Let me be clear".
"There is certainly enough for us to conduct an investigation", he added.
Mr Nunes said: "For the first time, the American people, and all the political parties now, are paying attention to the threat that Russian Federation poses".
One questioned "all of the contact with the Clinton campaign and the Russians".
Minutes later, Rep. Adam Schiff, the ranking Democrat on the intelligence committee, responded.
More than a dozen top lawmakers and intelligence officials have now said there's no evidence to support President Trump's tweet alleging that former President Obama wiretapped him.
". there is no evidence Potus colluded with Russia", Trump tweeted at 6:35 Monday morning.