Washington (CNN) Lawmakers on the House and Senate intelligence panels offered clashing opinions Sunday on the FBI's investigation into whether President Donald Trump's campaign and Russian officials colluded in an effort to influence the US election ahead of a House hearing on the issue.

House Intelligence Committee ranking Democrat Adam Schiff said on NBC's "Meet the Press" that he thought "there is circumstantial evidence of collusion" as well as "direct evidence" of deception.

"We need to know whether the circumstantial evidence of collusion and direct evidence of deception is indicative of more," said Schiff, of California.

Schiff's remarks are at odds with the statements of former Director of National Intelligence James Clapper, who said two weeks ago that he had not seen any evidence of collusion between the Trump campaign and Russia.

"I was surprised to see Director Clapper say that because I don't think you can make that claim as categorically as he did," Schiff said.

The congressman's comments came as his committee prepares to take testimony from FBI Director James Comey and National Security Agency Director Mike Rogers about the administration's investigation into Russia's attempts to influence the US election as well as any relationships between Russian officials and Trump's associates.

Sen. Tom Cotton on Sunday previewed the upcoming House hearing, saying Comey's testimony would address "unsubstantiated allegations" of dealings between Moscow and President Donald Trump's campaign.

"I do think it's important that we look at the broader context here," Cotton said on CNN's "State of the Union" with Jake Tapper. "The House committee hearing tomorrow is going to be in part about the unsubstantiated allegations in the media and by some Democrats of collusion between Trump associates and Russian intelligence."

The US intelligence community has said Russia was behind the hacks of the Democratic National Committee and former Hillary Clinton campaign chairman John Podesta, which it said were part of an effort to help Trump in the election. The Russian government has denied any wrongdoing.

CNN and others have reported that current and former law enforcement, intelligence and administration officials have said there were communications between Trump's associates and Russians known to US intelligence during the campaign.

Retired Lt. Gen. Michael Flynn resigned as Trump's national security adviser following media reports about his post-election communications with Russian Ambassador Sergey Kislyak.

However, House Intelligence Committee Chairman Devin Nunes said on "Fox News Sunday" that there was "no evidence of collusion" between Russia and the Trump campaign.

In his CNN interview, Cotton cited Clapper and former acting CIA Director Michael Morell, who have both publicly stated they also have seen no evidence of any collusion.

Morell, who supported former Secretary of State Hillary Clinton in the 2016 election, emphatically denied a connection between the Trump campaign and Russia earlier this month.

"On the question of the Trump campaign conspiring with the Russians here, there is smoke, but there is no fire," Morell said. "There's no little campfire. There's no little candle. There's no spark."

Wiretapping claims

As they took to the airwaves to offer differing opinions about the Russia matter, members of Congress almost all struck similar notes on Trump's unsubstantiated claim that President Barack Obama wiretapped his phones at Trump Tower in New York during the campaign.

Cotton, Nunes, House Speaker Paul Ryan and Maine Sen. Susan Collins were just some of Republicans who reiterated Sunday that they have seen no evidence Trump was correct about the accusation, which Trump and his administration have refused thus far to corroborate.

On Friday, the House Intelligence Committee received a classified report from the Department of Justice about the claim, which is all but certain to come up at Monday's hearing. At the time, sources told CNN that the report would not back Trump's accusation.

Nunes said Sunday that, based on his briefing with the Department of Justice, "there never" were physical wiretaps of Trump Tower, adding that a classified report from the department on Friday bolstered his belief that Trump was "literally" wrong.

The California Republican also said there was "no evidence of collusion" between Russia and the Trump campaign.

Cotton, a member of the Senate Intelligence Committee, said he had not seen any evidence to back Trump's wiretap claim, but he deflected a question from Tapper on whether the President should apologize to his predecessor if Comey says evidence for the President's accusation is lacking.

"We'll see what Director Comey testifies about," Cotton said.

Meanwhile, Sen. Ted Cruz seemed to back Trump, at least in spirit. The Texas Republican said on CBS' "Face the Nation" that Trump's accusation is "not necessarily outlandish" and accused the Obama administration of politically motivated behavior, citing the IRS scandal involving applications for tax-exempt status from conservative groups. But Cruz said Trump still needs to put forward the facts.

"It would be quite good for the administration to put forward what evidence there is," Cruz said.

The armed forces

Cotton, a veteran and member of the Senate Armed Services Committee, also touched on major military issues in the news.

Regarding the influx of Marines and other service members into Syria, Cotton did not advocate for a specific policy, but said, "I don't think we ought to set arbitrary troop caps."

The Arkansas Republican also called for the defeat of ISIS, but said the US needs to counter Iran, whose activities he blamed, in part, for the rise of ISIS.

"If we don't roll back Iran's gains throughout the region, we're not going to have stability, and we're not going to defend US interests to the degree that we should," Cotton said.

The senator also called the nude photo scandal in the Marine Corps, in which photographs of service members were taken and shared online without the subjects' consent, "extremely disappointing" and assured the public that those responsible would be identified and punished.

"I'm confident they're going to hold every Marine accountable," Cotton said, adding that he thought it was possible the scandal might extend beyond the Marines and could involve members of the Army, Navy and Air Force.