Mark Esper, who previously served as secretary of defense under former President Donald Trump, expressed grave concern on Saturday over the prospect of his former boss being reelected in November.

Trump is currently the overwhelming odds-on favorite to secure the 2024 GOP presidential nomination as he seeks a second term in the White House. Despite the four criminal indictments leveled against him, to which he has pleaded not guilty, Trump has remained popular with Republican voters, having won every state-level primary or caucus so far, aside from Nevada where he was not on the ballot. Only former South Carolina Governor Nikki Haley remains in the race against him.

With polling averages generally showing a toss-up in the general election between Trump and President Joe Biden, many observers and pundits have expressed concern over the destabilizing effect that another Trump presidency could have on the United States and the rest of the world. This has included statements from former members of his administration, like Esper, who discussed the possible ramifications of Trump’s reelection from a defense standpoint during a Saturday appearance on CNN.

Esper, who led the Department of Defense (DOD) from mid-2019 to late 2020, expressed concern in light of recent comments from Trump in which he denigrated Haley’s husband, a deployed member of the South Carolina Army National Guard, and suggested that he would not send assistance to fellow member nations of the North Atlantic Treaty Organization (NATO) without a financial incentive.

Former defense secretary Mark Esper is seen on July 9, 2020. Esper expressed concern on Saturday in light of Donald Trump’s recent comments about NATO and Nikki Haley’s husband.

Michael Reynolds-Pool/Getty Images

While speaking on Saturday to a crowd of supporters at a “Get Out the Vote” rally in Conway, South Carolina, ahead of the state’s GOP primary on February 24, Trump recalled telling a president of a NATO country that the U.S. would not protect them if they didn’t put more money into the military alliance.

“I said everybody’s gonna pay. They said, ‘Well if we don’t pay are you still going to protect us?’ I said, ‘Absolutely not.’ They couldn’t believe the answer. You’ve never saw more money poor in,” the former president said. “They asked me that question, one of the presidents of a big country, stood up, said, ‘Well sir, if we don’t pay and we’re attacked by Russia, will you protect us?’ I said, ‘You didn’t pay, you’re delinquent?’ He said, ‘yes.’ Let’s say that happened. No, I would not protect you, in fact, I would encourage them to do whatever the hell they want.”

Each member country contributes to NATO’s common funds. The amount that a given member contributes is based on its Gross National Income.

“He just sees it very transactionally, almost as if NATO is a country club and if you don’t pay your dues, then you don’t get to use the spa or you don’t get to golf,” Esper said. “That’s kind of how he approaches things.”

While Esper concurred with Trump on the argument that many NATO allies are not living up to their past commitments, a stance he said was held by many other former presidents as well, he stressed that exiting the alliance or threatening not to help other members fight against Russian aggression was the right answer. Esper also said that while he is not so sure Trump would allow Russia to invade a NATO ally, he does fear that Trump would cut support for Ukraine in its ongoing war with Moscow.

“I am concerned, I think it’s likely that if he returns to the White House, he will completely cut off support for Ukraine, and that will begin the slow collapse of the alliance behind Ukraine and lead to their increased vulnerability against Russia,” Esper said.

This, Esper worried, might also lead to Trump calling for U.S. NATO troops to be withdrawn from ally nations.

However, no U.S. president can unilaterally withdraw the country from NATO without congressional approval thanks to a provision in this year’s National Defense Authorization Act.

Newsweek reached out to Trump’s office via email for comment.

During his CNN appearance, Esper, who is a global affairs analyst for the network, also discussed Trump’s recent comments about Haley’s husband.

During Saturday’s rally, Trump brought up Haley’s husband, Michael, mocking the former governor of her spouse’s absence on the campaign trail.

“Where’s her husband? Oh, he’s away,” Trump said. “He’s away! What happened to her husband? What happened to her husband. Where is he? He’s gone.”

“It’s hard to understand why he would do that,” Esper said on Trump’s comments about Michael Haley. “What does he get from that, particularly in a pro-military state like South Carolina?”

Esper explained that Michael Haley has served honorably and is currently stationed in Djibouti in close proximity to Yemen, which he described as not a “cush” assignment. He also noted that former first lady Melania Trump has not been on the campaign trail with her husband, as Trump derided the Haleys for. During his time in the Trump administration, Esper said that military service was something the former president never “understood or appreciated.”

Update 2/11/24, 10:30 a.m. ET: This article has been updated with additional information.