Republican presidential candidate Nikki Haley on Sunday warned against taking “the side of a thug,” following former President Trump’s warning to NATO allies that he “would encourage” Russia “to do whatever the hell they want” to nations that are “delinquent.”

Asked by CBS “Face The Nation” anchor Margaret Brennan if she would adhere to the NATO premise that an attack on one is an attack on all, Haley — a former United Nations ambassador under Trump — said, “I mean, absolutely. NATO has been a success story for the last 75 years.”

Haley was responding to Trump’s comments from a Saturday rally in South Carolina, where he recounted a story about when an unidentified foreign leader questioned him over his threat not to defend members who do not hit the alliances defense spending targets.

Trump said he told the leader the would “encourage” Russia to do whatever it wishes and recalled saying, “‘You didn’t pay? You’re delinquent. No I would not protect you. In fact, I would encourage them to do whatever the hell they want. You gotta pay. You gotta pay your bills.’”

Haley on Sunday warned the U.S. against taking the “sides of a thug,” a likely reference to Russian President Vladimir Putin.

“But what bothers me about this is, don’t take the side of a thug, who kills his opponents. don’t take the side of someone who has gone in and invaded a country and half a million people have died or been wounded because of Putin. Don’t take the side of someone who continues to lie,” she continued, later pointing to her experience working with Russia.

“After September 10, we needed a lot of friends, we can never get into the point where we don’t need friends. Now, we do want NATO allies to pull their weight. But there are ways you can do that without sitting there and telling Russia, have your way with these countries,” she added later, in reference to the 9/11 attacks.

NATO’s secretary-general Jens Stoltenberg weighed in on Trump’s comments on Sunday, writing that “any suggestion that allies will not defend each other undermines all of our security, including that of the U.S., and puts American and European soldiers at increased risk.”

Haley — Trump’s main GOP presidential challenger — has repeatedly called out Trump’s apparent friendliness to foreign dictators on the campaign trail.

National polling indexes from The Hill and Decision Desk HQ show Trump with a 60-point lead nationally over Haley, while the former president has a 32- point lead in Haley’s home state of South Carolina.