The endorsement of Hillary Clinton by a former commander of U.S. Central Command has prompted Donald Trump to claim the retired four-star general is a “loser” for not figuring out a way to dodge his military obligations.

The Republican presidential nominee’s criticism of John Allen’s inability to duck out of his commitment to Uncle Sam followed the Marine general’s negative remarks about Trump at the Democratic National Convention in Philadelphia.

Trump called Allen, who served as commander of U.S. Forces Afghanistan for nearly two years, a “total lightweight” who was “too stupid” to weasel his way out of military service like the New York billionaire did during the Vietnam War.

“If a guy is not smart enough to get out of wearing a uniform, he’s certainly not smart enough to defeat ISIS.”

“They had a general I never heard of named John Allen at their convention who said some nasty things about me,” Trump told the crowd at a rally in Colorado Springs. “You know who he is? He’s a loser who was too stupid to get out of his commitment after graduating from the Naval Academy. That’s who he is.”

The real estate mogul was a decorated cadet who excelled as a football and basketball player at the New York Military Academy, from which he graduated in 1964. By the height of hostilities in Southeast Asia in 1968, Trump had received four deferments from military service, and he ultimately was declared medically disqualified just two months after his local draft board had classified him as “1A” (available for unrestricted military service).

Trump has since said he had bone spurs.

“If a guy is not smart enough to get out of wearing a uniform, he’s certainly not smart enough to defeat ISIS,” Trump said of Allen. “That’s why I know more than all the generals and will kick ISIS’ ass.”