“I don’t think that lying to get out of serving your country is patriotic. It’s not like there was just some empty seat in Vietnam. Someone had to go in his place,” Moulton said Sunday on MSNBC. “I’d like to meet the American hero who went in Donald Trump’s place to Vietnam. I hope he’s still alive.”

Buttigieg, speaking at a Washington Post Live event last week, said of Trump, “This is somebody who, I think it’s fairly obvious to most of us, took advantage of the fact that he was a child of a multimillionaire in order to pretend to be disabled so that somebody could go to war in his place.”

Buttigieg, 37, then made an overture to Republicans to reconsider their support of Trump, saying he was “old enough to remember when conservatives talked about character as something that mattered in the presidency.”

The flap could propel Democrats toward a more direct discussion of matters of war and service as the 2020 campaign intensifies. Following victories by several Democratic veterans during the 2018 elections, party leaders are putting an emphasis on the protection of diplomatic and military norms amid Trump’s shattering of them.