Can the U.S. rein in Russia's hacking?

President Donald Trump's tweet that he and Russian President Vladimir Putin discussed forming an "impenetrable Cyber Security unit" to prevent election hacking set off a firestorm of reaction from politicians and cybersecurity experts.

Administration officials came out in support of the idea, with Treasury Secretary Steve Mnuchin calling it an "important step forward" on ABC's This Week.

"What we want to make sure is that we coordinate with Russia, that we're focused on cybersecurity together, that we make sure that they never interfere in any democratic elections," Mnuchin said. "This is about having capabilities to make sure that we both fight cyber together."

The notion was largely dismissed out of hand by members of both parties, however, with a number of Republicans decrying the notion of partnering with the country that used cyber means to try to influence the U.S. election.

Sen. Lindsey Graham (R-S.C.) called it one of the dumbest ideas he had heard, and Sen. Marco Rubio (R-Fla.) likened it "to partnering with Assad on a 'Chemical Weapons Unit.'"

Then, as people were still in the process of denouncing Trump's mention of cyber partnership with Russia, the president reversed course and tweeted: "The fact that President Putin and I discussed a Cyber Security unit doesn't mean I think it can happen. It can't-but a ceasefire can,& did!" – referring to the ceasefire in Syria.

That, in turn, led to more head scratching and attempts to read between the lines as to whether Trump is seriously considering sharing cybersecurity information with Russia and whether or not at this point he believes Russia interfered in the election.

And, with Germany's parliamentary elections looming, it raises the question of what can and should be done to stop Russia's meddling in foreign elections.

"The consequences need to be identified and they need to be meaningful consequences in order to bring countries into the fold," said Megan Stifel, a senior fellow in the Atlantic Council's Cyber Statecraft Initiative who served on the National Security Council in the Obama administration.

Stifel said that the U.S. was successful in getting China to temper its cyber espionage because it drew a clear red line by indicting Chinese individuals and publicly calling out the country for stealing business secrets.

"We haven't in part found the right level to pull or draw the Russians into the fold, maybe there isn't one," she said, adding that in the past the U.S. was able to bring Russia to the table on nuclear treaties, and it is not clear if there is an equivalent mechanism today.

"If you're trying to identify kind of the low hanging fruit that might be of mutual interest between the countries as a way to kind of demonstrate trust, you could identify cybercrime," she said. "But the challenge is we've been trying to work with the Russians on cybercrime for decades and rather than arresting these guys, they recruit them and put them to work."

In addition, Stifel said the problem has been complicated by America's strained relations with key European countries. Some of those tensions started with the Snowden leaks about U.S. surveillance, but relations have further soured under Trump.

"Before we are able to make good progress with Russia I think we're going to have to heal some of our relationships with the like-minded that we need to draw into this," she said.

Stifel said that in the absence of strong U.S. leadership to punish Putin, it could be up to European countries to decide they have had enough of Russia interfering in their democracies that they collectively say to the Kremlin, "you need to stop this or else."

Either way, she said, some confluence of forces needs to make it "so painful for the Russians that they decide it's not worth this interference anymore."

"At this point, I don't think that it can happen without U.S. leadership, but that's I think where we are," she said.