Trump now says Russia-US cybersecurity unit can't happen President seems to change his tune on the idea.

 -- President Trump seemed to change his tune on a cybersecurity unit that he discussed with Russian President Vladimir Putin this evening, saying just because the two discussed it "doesn't mean I think it can happen," adding that "it can't."

In a series of tweets Sunday morning about his G-20 meeting with Putin, Trump said it was time to work "constructively with Russia," and said that he and Putin "discussed forming an impenetrable Cyber Security unit so that election hacking, & many other negative things, will be guarded."

But the president faced backlash even from members of his own party about the idea of teaming up with Putin on cybersecurity. Florida Sen. Marco Rubio tweeted earlier that such a partnership "is akin to partnering with [Syrian President] Assad on a Chemical Weapons Unit."

Treasury Secretary Steven Mnuchin, when asked about Rubio's comments on ABC News' "This Week" today, defended the idea of a joint Russian-U.S. cybersecurity unit, calling it "a very significant accomplishment."

"Well, in all due respect, and I think very highly of the senator, but let me just comment on that. I think this is a very important step forward that 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 or conduct any cybersecurity," he said.

"And this is like any other strategic alliance, whether we're doing military exercises with our allies or anything else. This is about having capabilities to make sure that we both fight cyber together, which I think is a very significant accomplishment for President Trump," Mnuchin said.