Former CIA Director John Brennan said Wednesday that he finds it “implausible” that Americans did not help Russian operatives interfere, either “wittingly or unwittingly,” in the presidential campaign last year.

During an event at Fordham University, Brennan was asked by NBC’s Andrea Mitchell whether he believed that Russians could have figured out how to target areas in swing states like Michigan and Wisconsin without the help of Americans, including in the Trump campaign.

“Is it your theory of the case that there was some connection between the campaign and the Russian operations?” Mitchell asked.

“It’s hard for me to believe that the Russians, as good as they are, as sophisticated as they are, a program like this, were not able to get some Americans to cooperate with them, either wittingly or unwittingly,” said Brennan.

“I find it implausible,” the Obama administration official added.

While at the CIA, Brennan signed on to an intelligence assessment produced by the Office of the Director of National Intelligence which attributed email hacks against Democrats to Russian government operatives. Brennan and other intelligence community officials have said that they believed that the Kremlin had two goals: to undermine the U.S. democratic process and to hurt Hillary Clinton’s chances of winning the election.

It has since emerged that Kremlin-connected groups used social media platforms like Facebook and Twitter to publish propaganda aimed at sowing discord in the American public, though the effectiveness of that operation is unclear.

In May, Brennan testified to the House Intelligence Committee that he “encountered” and was “aware of” intelligence and information showing contacts between Russian officials and members of the Trump campaign.

He said he was “concerned” about those contacts “because of known Russian efforts to suborn such individuals.”

“It raised questions in my mind about whether Russia was able to gain the cooperation of those individuals,” said Brennan, who did not name which Trump campaign associates had made contact with Russians.

“I don’t know whether such collusion existed,” he added.

WATCH:

Follow Chuck on Twitter