Former Democrat presidential candidate and avid Trump critic Hillary Clinton warned that if elected Donald Trump will make good on his threat to withdraw the U.S. from NATO.

Over the weekend, Clinton made the claim during remarks at the Munich Security Conference in Germany, telling U.S. allies that they should take Trump’s claims to heart after the former president warned NATO countries to contribute their fair share.

“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. 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.”

“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.

Clinton seemed to direct her message to NATO Secretary General Jens Stoltenberg, who has brushed off Trump’s recent comments.

The Republican presidential frontrunner has repeatedly claimed that member countries should not receive protection if they do not pay their share toward NATO’s budget.

“The whole idea of NATO is that an attack on one ally will trigger a response from the whole alliance and as long as we stand behind that message together, we prevent any military attack on any ally,” Stoltenberg said.

“Any suggestion that we are not standing up for each other, that we are not going to protect each other, that does undermine the security of all of us.”

According to Fox News, the NATO chief announced that 18 of the alliance’s 31 members are on track to meet their pledges of contributing 2% of GDP to the group. European states are on track to contribute $380 billion this year, and Germany will meet its 2% pledge for the first time since the Cold War.