A veterans activist says Donald Trump's latest comment about Sen. John McCain's, R-Ariz., war hero status will irreversibly damage his appeal among veterans.

During an appearance on Fox News Channel's "The Greg Gutfeld Show" Sunday evening, Iraq and Afghanistan veteran Amber Smith said Trump's remarks were "pure ego" and demonstrated "how [he] really feels about America's veterans and our current military."

"I think that that's what people originally liked about Trump when he first joined the race, is they're like 'Oh, he's going to say what everybody else is thinking and that's what we like about him, is he tells it like it is.' But don't go after America's veterans. How dumb do you have to be?" Smith said, according to Breitbart.

The former Army helicopter pilot, who now serves as senior military adviser for the nonprofit Concerned Veterans for America, described the Republican presidential hopeful's comments as both "political suicide" and a red flag that he is "not commander in chief material."

The show's host, Greg Gutfeld, added that the real estate tycoon "finally gave the RNC the open door to go in and say, 'Enough. We've had your fun.'"

Trump's rivals in the GOP primary field have been quick to condemn the billionaire businessman's remarks. Florida Sen. Marco Rubio called them "absurd," "offensive," and "ridiculous" during an interview Sunday on CNN; former Texas Gov. Rick Perry said Trump should "immediately withdraw from the race;" and the RNC issued a statement saying "there is no place in our party or our country for comments that disparage those who have served honorably."

Despite facing tremendous backlash, Trump has so far refused to apologize for his jab at the Arizona senator. He penned an op-ed in USA Today doubling down on his McCain criticism and saying he didn't want to be lectured by his opponents.