Former CIA director John Brennan testifies before the House Intelligence Committee to take questions on “Russian active measures during the 2016 election campaign” in the U.S. Capitol in Washington, U.S., May 23, 2017. Kevin Lamarque/Reuters Former CIA Director John Brennan, in testimony Tuesday before the House Intelligence Committee, said that he was concerned by some of the "interactions" between Russian officials and members of the Trump campaign that took place during the election last year.

Brennan's testimony on Russian interference in the election came two months after he was originally scheduled to testify in an open hearing that was unexpectedly canceled by the committee's chairman, Rep. Devin Nunes. He told the committee that he warned his Russian counterpart, FSB chief Alexander Bortnikov, in an August 2016 phone call against interfering in the presidential election.

"It should be clear to everyone that Russia brazenly interfered in our 2016 presidential election process," Brennan said in his opening statement, "and that they undertook these activities despite our strong protests and explicit warning that they do not do so."

Republican Rep. Tom Rooney asked Brennan if he ever found "any direct evidence of collusion between the Trump campaign and Putin in Moscow" while he was the CIA director.

Brennan replied that "there was intelligence that the Russian intelligence services were actively involved in this effort ... to try to get individuals to act on their behalf either wittingly or unwittingly." He added that he was "was worried by the contacts that the Russians were having with US persons" and "had unresolved questions" by the time he left office about whether" the Russians had succeeded in getting Americans to do their bidding.

Democratic Rep. Adam Schiff, ranking member of the committee, asked Brennan whether he was concerned by reports that Trump shared classified information with Russian diplomats during a meeting in the Oval Office on May 10.

"If the reports are true that the president decided to share classified intelligence with the Russians, then he violated two protocols," Brennan replied. "The first is that this kind of intelligence is not shared with visiting foreign ministers or local ambassadors. It's shared through intelligence channels. The second is that, before sharing any classified intelligence with foreign partners, it has to go back to the originating agency to ensure that revealing it won't compromise sources, methods, and future collection capabilities."

Brennan also said he was disturbed by the leaks coming out of the White House, especially the one that identified Israel as the apparent source of the intelligence Trump shared.

Rep. Trey Gowdy asked Brennan, again, whether he had seen evidence of collusion between the Trump campaign and Russia. Brennan replied: "I don't do evidence."

Pressed further, however, Brennan said that "the information and intelligence revealed contacts and interactions between Russian officials and US persons involved in the Trump campaign that I was concerned about because of known Russian efforts to suborn such individuals. It raised questions in my mind about whether the Russians were able to gain the cooperation of such individuals."

Former CIA director John Brennan testifies before the House Intelligence Committee to take questions on “Russian active measures during the 2016 election campaign” in the U.S. Capitol in Washington, U.S., May 23, 2017. Kevin Lamarque/Reuters

Brennan said he doesn't know if collusion ever occurred, but he said that he saw "information that was worthy of investigation by the [FBI] to determine whether such collusion took place."

"People on a treasonous path ....don't always realize they're on that path until it's too late," Brennan said. He added that the House Intelligence Committee "now has access to the type of information I'm alluding to here."

Brennan later confirmed to Democratic Rep. Mike Quigley that it wasn't just the fact that Trump campaign officials communicated with Russians that concerned him — it was which Russians the Trump associates spoke to.

That, in addition to the "backdrop" of Russia's election interference, raised Brennan's concerns about the communication that occurred between Trump campaign associates and Russia, he said.

Democratic Rep. Eric Swalwell asked Brennan whether he knew if any of the US persons who spoke to the Russians either made "false statements" about those contacts or failed to disclose them. Brennan replied that he thinks "that's something we can pursue in a closed session."

The hearing was held one day after Democratic Rep. Elijah Cummings, ranking member of the House Oversight Committee, announced that he had obtained evidence that Trump's former national security adviser, Michael Flynn, misled Pentagon officials about his contacts with Russians when he was renewing his security clearance in early 2016.

Michael Flynn Win McNamee/Getty Images

The Washington Post also reported on Monday that Trump had asked Director of National Intelligence Dan Coats and National Security Agency Director Adm. Mike Rogers to publicly rebuke former FBI Director James Comey's testimony on March 20 that the Trump campaign was being investigated for possible collusion with Russia.

Republican Sen. John McCain asked Coats during a separate Senate Armed Services Committee hearing on Tuesday whether the Post report was true. Coats declined to answer the question directly, but did not deny that Trump made the request.

"I don't feel it's appropriate to characterize discussions and conversations with the president," Coats said, noting that he and Trump "discuss a number of topics on a very regular basis."

Trump fired Comey earlier this month, just over nine months into the FBI's probe of Russia's hacking and disinformation campaigns that targeted Democrats during the election. That probe began in earnest when Robert Hannigan, then the chief of Britain's Government Communications Headquarters, passed Brennan material related to conversations Trump associates had with suspected or known Russian agents in late 2015 and early 2016, according to The Guardian.

Brennan was so concerned about the intercepted communications that he established a counterintelligence task force, which included the FBI and the National Security Agency. (Former Director of National Intelligence James Clapper testified earlier this month that those communications had been picked up and handed over to US agencies, but he could not elaborate due to the "sensitive" nature of the intelligence.)

"We set up a group within the CIA, and I spoke with [FBI Director] Comey and [NSA Director] Rogers to get their best people involved so that they could share information" with the agency. Brennan said he "wanted to make sure that there would not be any barriers" to sharing information between intelligence and law enforcement officials.

In August — more than eight months after British officials were alerted to the Trump-Russia contacts — Brennan briefed the US's top lawmakers on the material, which he said showed that Russia had interfered in the US election to help Trump win, The New York Times has reported.

Around the same time, former British spy Christopher Steele was collecting intelligence from his sources in Moscow about Russia's attempts to cultivate Trump and his associates as foreign assets in their mission to undermine Clinton. Brennan told Gowdy he didn't know who commissioned the Steele dossier, but he asserted that it was "not in any way used as the basis for the intelligence community's assessment" in January that Russia interfered in the election to help elect Trump.

Democratic Rep. Jackie Speier asked Brennan about Russian oligarchs investing in the United States, and whether he was aware of efforts by the Russians to cultivate Trump while he was a real estate developer.

Brennan replied that he could not comment. But he noted later that the Russians have long engaged in money laundering "in a number of countries" and that the intelligence community has seen more collaboration recently between Russian intelligence services and organized criminals.

Democratic Rep. Denny Heck asked Brennan to tell the committee "why my constituents should care" about Russia's election interference. "Why do you care, sir?"

"Because for the last 241 years, this nation and its citizens have cherished the freedom and liberty that this country was founded on," Brennan replied.

"Our ability to choose our elected leaders as we see fit is, I believe, an inalienable right we must protect with all of our resources and all our authority and power," he continued. "And the fact that the Russians tried to influence the election so that the will of the American people was not going to be realized by that election, I find outrageous, and it is something that we need to resist."