Erin Kelly

USA TODAY

WASHINGTON — Former CIA director John Brennan said Tuesday he doesn't know whether there was collusion between the Trump campaign and Russian officials in the 2016 election, but he left office in January with "unresolved questions" about whether Russia had been successful in getting Trump campaign officials to act on its behalf "either wittingly or unwittingly."

"I encountered and am aware of information and intelligence that revealed contacts and interactions between Russian officials and U.S. persons involved in the Trump campaign that I was concerned about because of known Russian efforts to suborn such individuals," Brennan testified before the House Intelligence Committee. "It raised questions in my mind about whether Russia was able to gain the cooperation of those individuals."

"I don't know if such collusion — your words — existed," Brennan told the committee. "I don't know. But I know there was sufficient intelligence ... to warrant investigation by the (FBI)."

Brennan's testimony came in the wake of President Trump's firing of FBI Director James Comey two weeks ago as Comey was in the midst of investigating possible collusion between the Trump campaign and Russian officials. Last week, Deputy Attorney General Rod Rosenstein appointed former FBI Director Robert Mueller to act as a special counsel to investigate any possible collusion.

Pressed by committee members on what "evidence" he has of any collusion between the Trump campaign and Russian officials, Brennan said he has no evidence but has intelligence that he shared with the FBI, which used it as a basis for its investigation. He said the CIA is in the business of gathering intelligence, not evidence.

Brennan declined to identify Trump campaign officials who had contact with Russian officials, saying that the information was classified and had been provided to the committee on a classified basis.

He said that Americans don't always know when they're helping Russian spies because Russian intelligence agents often use intermediaries.

"Many times (Americans) do not know that the individual they are interacting with is a Russian,” Brennan said.

The former CIA director warned that he does not believe the Russians are done trying to interfere in America's elections and could try to influence the 2018 congressional elections.

"I believe that they will try to exploit elections," he said, adding that he has "grudging respect" for Russia's intelligence efforts. "The Russian intelligence threat is a serious one."

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Beyond elections, Russian President Vladimir Putin will undoubtedly try to exploit political chaos and divisions in Washington, Brennan said.

"The Russians are watching very carefully what is going on in Washington right now, and they will try to use if for their purposes," he said. "Mr. Putin and Russian officials are trying to actively exploit what is going on now in Washington to their benefit and to our detriment."

Brennan also said that, if press reports are accurate, Trump may have violated two major protocols governing the sharing of classified information when he spoke with Russian diplomats in the Oval Office on May 10. The president reportedly shared intelligence information from Israel about ISIS to the Russians. Trump has defended his disclosure, saying he had the right to share the information.

Brennan said protocol requires that any sharing of classified information with foreign governments be done through intelligence channels, not from the president to visiting officials. He said any information that is shared also needs to be cleared by the agency where the intelligence information originated.

He said it "appears from press reports that it (the intelligence Trump shared) didn't go through proper channels."

Brennan said he warned the head of Russian intelligence, Alexander Bortnikov, in a phone call last year that Russian interference in the U.S. presidential election would severely damage U.S.-Russian relations.

"I said American voters would be outraged by any Russian attempt to interfere in our elections," Brennan said. He said he told Bortnikov that Russian interference "would destroy any near-term prospect of improvement" in the relationship between the U.S. and Russia.

Brennan said Bortnikov denied that Russia was meddling in the U.S. presidential election and said he would inform Putin of Brennan's comments.

"I believe I was the first U.S. official to brace Russia on this matter," Brennan said.

Brennan continued briefing the committee in closed session after the public hearing.

The House Intelligence Committee is one of four congressional committees investigating Russian interference in the 2016 presidential election and possible collusion between the Trump campaign and Russian officials.

Rep. Adam Schiff of California, the senior Democrat on the House Intelligence Committee, said Brennan's testimony underscored that it's important for Congress to continue conducting its own investigations even though Mueller has been appointed to lead the FBI probe.

"(Tuesday's) testimony by former CIA Director Brennan that the Russians brazenly interfered in our election, and that he became aware of interactions between Trump campaign officials and the Russians that warranted referral to the FBI further underscores the importance of our investigation," Schiff said. "Moreover, the director's admonition that the sharing of any classified information with the Russians should only proceed through intelligence channels, and with significant thought given to ensuring that whatever information is provided would not reveal sources and methods, should serve as a reminder to the White House of the dangers of any impromptu disclosures by the President."

Brennan said he was concerned about leaks from the president's Oval Office meeting with the Russian officials.

"What I was very concerned about ... is the subsequent releases of what appears to be classified information purporting to point to the originator of the information, liaison partners," Brennan said, referring to press reports that the classified information came from Israel. "They continue to be very, very damaging leaks and I find them appalling and they need to be tracked down."