Former Director of National Intelligence James Clapper James Robert ClapperOn China, Biden is no Nixon — and no Trump The Hill's 12:30 Report - Speculation over Biden's running mate announcement Trump slams former intelligence officials to explain 'reluctance to embrace' agencies MORE on Tuesday said Russia's “aggressiveness” in interfering in last year's U.S. presidential election was unlike anything he'd seen before.

“Across the board, the aggressiveness in this campaign was unprecedented,” Clapper told CNN’s “New Day.”

“An American citizen should be very concerned about a foreign government, particularly our primary adversary, interfering with the most important foundational process that we have in this country, which is free and fair elections.”

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Clapper noted that the Russians have long tried to interfere in presidential elections, but characterized their 2016 efforts as the most aggressive and direct.

“There’s been a long history of ... interference, going back to the Soviet era, in our elections,” Clapper said. “But never ever has there been a case of the aggressiveness and the direct actions that the Russians took and their conduct of a multifaceted campaign to interfere with our election.”

Not only did the efforts include the hacking of political organizations, Clapper added, but also “very sophisticated, slick propaganda efforts.” He specifically cited Kremlin-run media outlet RT as playing a central role.

Clapper, who has testified in front of Congress as it investigates Russia’s efforts to interfere in the election, said now is the time for vigilance.