Some three years ago, as the 2016 race for president was gearing up, Sam Nunn had a message for the assembling candidates: President Barack Obama had gone too far in severing ties with Vladimir Putin and Russia over the invasion of Ukraine.

The former U.S. senator’s reasoning was simple. Nuclear powers are more dangerous when isolated.

So the question for Nunn on Tuesday was obvious: Was President Donald Trump’s performance at the Helsinki summit anything close to what he had in mind?

In a word, no.

John Brennan, the former CIA director, has employed the word “treasonous” to describe Trump’s very public decision to side, literally and figuratively, with Putin on a situation that has achieved unanimous agreement among U.S. intelligence agencies and the Department of Justice: That Russia tried to bend the ’16 presidential contest in Trump’s favor.

Even former U.S. House speaker Newt Gingrich, a Trump loyalist, called Trump’s remarks “the most serious mistake of his presidency.”

In our telephone interview, Nunn stuck to his own vocabulary. “Baffling” was one word. “Very disturbing” passed his lips. But ever the organized thinker, Nunn divided the Trump-Putin meeting into four categories: The good, the bad, the ugly and the unknown.

To understand Nunn’s starting point, remember that he’s built his post-congressional career (he left the U.S. Senate in 1997 and will turn 80 in September) around defusing the threat of loose nukes in a collapsed Soviet Union. That has been the work of the Washington-based Nuclear Threat Initiative. He’s a co-founder (with Ted Turner) of the organization, and is now co-chair with former energy secretary Ernest Moniz.

Which means Nunn is ever quick to connect the state of U.S.-Russia relations to the survival of humankind.

"On the good side, the president did address the strategic stability of nuclear weapons. That's the primary responsibility of both presidents. The United States and Russia have 90 percent of the world's nuclear weapons and nuclear material," Nunn had said on Bloomberg TV just a few minutes before we talked.

This is an argument that was also made Tuesday by David Perdue, who now holds the Georgia seat that Nunn once did in the Senate. But Perdue stopped there. His predecessor didn't.

During our conversation, Nunn was quite concise about the “bad” and “ugly.” There was Trump’s denigration of our NATO allies at last week’s meeting in Brussels, and the description of the European Union as an economic “foe.” Followed by Trump’s decision on Monday to favor the “extremely strong and powerful” denial of interference by Putin over his own intelligence agencies.

“There certainly has been some damage done to America’s national security, in terms of undermining our law enforcement community and our intelligence community,” Nunn said. There’s a piper to be paid for both mistakes, and the bill could be steep.

Trump attempted to backpedal on some of his statements Tuesday, but words uttered on the world stage are hard to unsay.

Even so, Brennan’s use of the word “treasonous” to describe Trump’s behavior the day before is problematic, if only because such an action involves intent. I asked Nunn whether he thought the president’s behavior to be purposeful, or the result of mere incompetence.

“The only thing I can guess,” Nunn said, “is that President Trump is so obsessed with his own election legitimacy that everything else, no matter how important, seems to be blocked out. That just takes the first ten spots on his mental approach. That’s the only thing I can figure out. It’s baffling.”

As he watched video of Trump, Nunn said a certain Marx Brothers line came to mind: “Are you going to believe me or your own eyes?”

The unknown portion of the Trump-Putin meeting is another worry. That explosive press conference was preceded by a two-hour meeting between the two leaders, with no aides in attendance — only translators.

Mark Warner, the Virginia Democrat, has suggested bringing the U.S. interpreter before a Senate committee to figure out what went on. Nunn doesn’t think that will work — a presidential claim of executive privilege would likely check the effort.

As it stands, even Secretary of State Mike Pompeo can’t tell Congress what the two leaders talked about. “I assume that’s the purpose of not having anyone else in the room,” Nunn said.

The former Georgia senator called for Republican members of Congress to move beyond the “creeping candor” that they’ve used to gently criticize President Trump — not just on foreign policy, but on the issue of trade as well.

But if Congress wants to become an active overseer of U.S. policy toward Russia, more engagement is needed. In that Bloomberg interview, Nunn called for the creation of a small House-Senate committee to coordinate with the State Department and Pentagon.

”We don’t want the secretary of state, secretary of defense and other key administration officials to be hobbled in terms of the diplomacy they must discuss with the one nation on earth that can basically destroy the United States, albeit at the expense of their own destruction,” Nunn said.

I asked Nunn if he were recommending that Congress take control of U.S. foreign policy. He said no. His point was that Congress has already taken control of a large portion of U.S. policy toward Russia, but hasn’t yet absorbed the implications.

Last year, Congress voted nearly unanimously to pass a law setting sweeping new sanctions on Moscow — and eliminating the president’s power to issue waivers.

“I understand the reason they did it, because both Republicans and Democrat don’t have confidence in President Trump,” Nunn said. “But when you take on that responsibility, you have gravely hobbled the executive branch. If the Russians conclude they will never have a get-out-of-jail card, you’re incentivizing bad behavior.”

Because the power has been taken out of Trump’s hands, Congress must make clear what diplomatic path Russia must take to escape those sanctions. “Congress has to step up to the plate and assume responsibility equivalent to their action,” Nunn said. “Congress has dealt itself a hand, and right now, it’s not organized to play that hand.”

In other words, someone needs to talk to Russia. And if Trump can’t be trusted, that job falls to Congress.