Former Secretary of State Hillary Clinton warned Saturday that former President Donald Trump will seek to withdraw the U.S. from NATO if he wins a second term in the White House.

In remarks during a lunchtime panel at the Munich Security Conference, Clinton urged delegates to take Trump “literally and seriously” as he seeks re-election.

“We have a long struggle ahead of us, and the obvious point to make about Donald Trump is take him literally and seriously,” she said.

“He means what he says,” she continued. “People did not take him literally and seriously in 2016. Now he is telling us what he intends to do, and people who try to wish it away, brush it away, are living in an alternative reality.”

Clinton, who unsuccessfully ran against Trump in the 2016 presidential election, also warned Saturday that the former president will seek to “pull us out of NATO.”

“He will do everything he can to become an absolute authoritarian leader if given the opportunity to do so. And he will pull us out of NATO even though the Congress passed a resolution saying that he couldn’t without congressional support, because he will just not fund our obligations,” she said.

Trump has come under fire for recent comments he made about not protecting NATO countries, saying during a rally in South Carolina that he would let Russia “do whatever the hell they want” if it attacked a NATO country that was late on payments to the alliance.

The chairman of the Joint Chiefs of Staff, Gen. Charles Q. Brown Jr., last week said that U.S. “credibility is at stake” with each of its alliances, including NATO, in response to Trump’s disparaging remarks.

“This year is the 75th anniversary of NATO,” Brown said in an interview with NBC “Nightly News” anchor Lester Holt last week. “And I think we have a responsibility to uphold those alliances. U.S. credibility is at stake with each of our alliances, and U.S. leadership is still needed, wanted and watched.”

NATO Secretary-General Jens Stoltenberg, however, said he is “confident” that the U.S. will “remain a strong ally and committed ally” regardless of the outcome of the November presidential election.