"I said American voters would be outraged by any attempt to interfere in the election", he added.
The top two members of the Senate intelligence committee say they will "vigorously pursue" the testimony of President Donald Trump's first national security adviser, even though Michael Flynn has invoked his Fifth Amendment right against self-incrimination.
The Washington Post, which broke the story, said that Trump revealed to Russian officials secrets about Islamic State capabilities.
"It raised questions in my mind, again, whether or not the Russians were able to gain the cooperation of those individuals", he said.
"I saw interaction that in my mind raised questions of whether it was collusion", Brennan told Rep. Trey Gowdy, saying that he supported the Federal Bureau of Investigation digging further. Brennan had become so concerned about the possibility of a Russian intervention a year ago that he had high level meetings with top officials to brief them about the nature and extent of Russia's interference.
Comey was sacked May 9, and news reports since have said that Trump asked Comey on multiple occasions to drop the investigation into Trump's first national security adviser, Michael Flynn, who had dined with Russian President Vladimir Putin in 2015, two months before he became Trump's primary foreign-policy adviser.
Brennan said that it is likely Russian Federation had thought it could have better relations with the USA under Trump, a political outsider and businessman, and noted the "animus" that had built between Clinton and Putin over the years.
In congressional testimony, Brennan said that such meddling "would destroy any near-term prospect of improvement" in relations between the United States and Russian Federation. Brennan said it was possible for someone to be helpful to the Russian cause without realizing it.
The Justice Department says Robert Mueller's work at a law firm that represented relatives and associates of President Donald Trump does not disqualify him from overseeing an FBI investigation into possible ties between Trump's presidential campaign and Russian Federation.
Former CIA Director John Brennan says he thinks Russian Federation cooperates with WikiLeaks through middlemen. If Russia had collected more information about Clinton that they did not use against her during the campaign, Brennan said they were likely "husbanding it for another day".
But Brennan told the House intelligence committee on Tuesday that President Donald Trump would have violated protocol if he shared such information with Russian officials in the Oval Office spontaneously.
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Brennan, who departed as Central Intelligence Agency chief when Trump took office in January, said he believed he was the first USA official to raise the matter of election interference with the Russians, citing an August 4, 2016 phone call he had with the head of Russia's FSB security service, Alexander Bortnikov.
Trump has defended his disclosure, saying he had the right to share the information. He said there appear to be "very, very damaging leaks, and I find them appalling and they need to be tracked down".
But Brennan's testimony in regard to his suspicions about the possibility of collusion is broadly consistent with what a number of other high-profile voices - former acting deputy Attorney General Sally Yates, former FBI Director James Comey - have said: That the ties between Russian Federation and the Trump campaign deserve more investigation.
"The cyber-environment now really provides so much more opportunity for troublemaking and the Russians take advantage of it", he said.
Brennan said that people aren't always aware that they are interacting with Russian intelligence operatives, or that they are a target in a Russian influence campaign.
He said Russian Federation used WikiLeaks as a "cut-out", or go-between, and that protests by WikiLeaks that it is not working with Russian Federation and Russia's claims it is not working with WikiLeaks are "disingenuous".
Brennan said that while he was Central Intelligence Agency director he shared classified information with Russian Federation and other nations about threats related to terrorism. Prior to that, Brennan was a top counterterrorism and homeland security adviser to Obama.
House Oversight Committee Chairman Jason Chaffetz says he will postpone a hearing scheduled for Wednesday after speaking with former FBI Director James Comey. After pressure from Democrats, Nunes has turned over leading the committee's Russian Federation investigation to Rep. Mike Conaway, R-Texas, who is also a CPA.
Brennan continued briefing the committee in closed session after the public hearing.
He was asked about a Washington Post that said Trump asked Coats and Michael Rogers, the director of the National Security Agency, to push back against an FBI investigation that's been examining potential coordination between Moscow and the presidential campaign.
The Senate panel on Tuesday chose to issue two additional subpoenas to Flynn's businesses and sent the letter to his lawyer asking about the legal basis for his invoking his Fifth Amendment right over documents as opposed to testimony.