If Donald Trump were elected president, he would become commander-in-chief. Like so many previous presidents, it’s likely he’d need to send U.S. troops into harm’s way at some point. That’s why his incendiary, insulting depiction of Sen. John McCain’s wartime service to our country should be taken seriously, even if most Americans don’t want to take Trump himself seriously.

Riding high in GOP polls, Trump took the low road at a forum in Iowa on Saturday when he said of McCain: “He’s not a war hero. He’s a war hero because he was captured. I like people who weren’t captured.”

Trump (who avoided the draft due to a medical deferment) and his supporters shouldn’t need a reminder of McCain’s sacrifices. But here’s a brief recap: McCain, a naval aviator during the Vietnam War, was shot down, held in Hanoi for five years and, despite being tortured, refused release ahead of his comrades.

He and other POWs — including many Minnesotans who were held during Vietnam and other wars — are not only heroes, they’re owed a debt a grateful nation can never truly repay. There is a reason that POW/MIA flags still fly. Most Americans recognize and respect the sacrifices made by all veterans, but especially those who, in Trump’s words, were captured.

Most GOP opponents and some party officials have finally denounced Trump’s latest bout of idiocy. While that’s welcome, it should not have taken such a blatant breach of decency to spur them on. Trump’s racist characterization of undocumented Mexican immigrants as criminals and “rapists” was reason enough. Other statements, as well as his intellectually lazy approach to the world’s most consequential job, have destroyed whatever credibility he brought to the race.

Trump will take one of the coveted spots in upcoming GOP debates that will be limited to candidates polling in the top 10. Although he has a right to run for president, GOP leaders — as well as voters — have a responsibility to hold him accountable for his counterproductive candidacy.