“I think ISIS can do terrible things. But it’s the Russians who tried to destroy the fundamental of democracy and that is to change the outcome of an American election,” McCain told ABC News Australia.

“They just tried to affect the outcome of the French election,” McCain continued. “So I view Vladimir Putin — who has dismembered Ukraine, a sovereign nation, who is putting pressure on the Baltics — I view the Russians as the far greatest challenge that we have.”

Although McCain told the Australian outlet he hasn’t seen evidence that Putin had succeeded in interfering with the U.S. election, he did say he thinks the Senate should impose sanctions on Russia.

The Arizona senator also addressed reports that White House Senior Adviser Jared Kushner, who is also the President’s son-in-law, worked to establish a backchannel of communications with the Kremlin during the transition period.

“I don’t like it, I just don’t,” McCain said. “I know some administration officials are saying this is standard procedure. I don’t think it’s standard procedure prior to the inauguration of the President of the United States by someone who is not in an appointed position.”

McCain also acknowledged that President Trump made him nervous at times, because he doesn’t always accept recommendations from his national security team.