Former Trump defense secretary Mark Esper on Sunday expressed concern over how President Biden’s debate performance was perceived on a world stage, suggesting it could sew doubt within foreign allies and adversaries about his ability to serve.

“I mean, it’s very, very serious. I mean, if you’re a foreigner, an ally or a partner, you’re looking at this and you start questioning…Does he have the stamina to go another four years?” Esper said on CNN. “And look, you can’t help but answer and say, no.”

Biden is facing increased scrutiny following his poor debate performance against former President Trump last week. The performance sparked panic among some Democrats over his ability to win reelection and lead the nation for another four years.

Esper, who served in the Trump administration for nearly two years, has said he will for vote for his former boss in November. But he suggested Biden is going to get progressively worse over time.

“We know what he’s wrestling with…we see it unfortunately, in our parents or grandparents and every day, every week, he’s going get a little bit worse,” he said.

“And the question is, at a time when the world needs America’s leadership in the era of great power competition, where the autocracies of Russia and Iran and North Korea are lining up against the Western democracy, American leadership matters…. The commander in chief of the United States is also important,” he continued.

Esper argued it is also important to ask if America’s adversaries, such as Chinese President Xi Jinping and Russian President Vladimir Putin, see “weakness” in Biden.

Some GOP members, including House Speaker Mike Johnson (R-La.), have suggested Biden’s Cabinet should consider removing him under the 25th Amendment, citing U.S. adversaries whom he said “seek the weakness in this White House.”

The 25th Amendment to the Constitution, which governs presidential succession, says that the vice president and a majority of the Cabinet may vote to declare a president “unable to discharge the powers and the duties of his office” and give the vice president the duties of acting president.

Despite calls from an increasing number of Democratic voters and pundits — and some unnamed lawmakers — to withdraw from the presidential race, Biden and the White House insist the president will not step aside.

Biden has already won the primary and thus cannot be overthrown at the Democratic National Convention in August unless he agrees to bow out.