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While testifying Tuesday before the House Intelligence Committee, former CIA Director John Brennan revealed that FBI intelligence uncovered "contacts and interactions" between Russian officials and individuals involved with the Trump campaign. Brennan said he had grown "concerned" that those individuals may have been influenced to act on behalf of the Russian government.

Those worries persisted when he stepped down as CIA director on Jan. 20, Brennan testified. "I had unresolved questions in my mind, as to whether or not the Russians had been successful in getting U.S. persons involved in the campaign or not to work on their behalf again, either in a witting or unwitting fashion," Brennan said, calling the FBI investigation into Trump associates and Russians "well-founded."

Though he's certain that "Russia brazenly interfered in the 2016 election process," Brennan noted he does not "know whether such collusion [with Trump associates] existed."

Brennan said he explicitly warned Russia against meddling in the U.S. presidential election in a phone call on Aug. 4 to the head of the Russian intelligence service. Brennan testified that he'd threatened such interference would "destroy any near-term prospect of improvement" in U.S.-Russia relations. "I believe I was the first U.S. official to brace Russia on this matter," Brennan said.