AMES, Iowa » Republican presidential candidate Donald Trump criticized Sen. John McCain’s military record at a conservative forum Saturday, saying the party’s 2008 nominee and former prisoner of war was a "war hero because he was captured. I like people who weren’t captured."

The comment drew some boos from some in the audience — and quick condemnation from rivals who have been waiting for such an opening to rein in the outspoken reality television personality. Trump has surged in polls recently, frustrating many in his party concerned that he has hijacked the 2016 Republican primary and damaged the GOP brand.

Trump and McCain traded barbs earlier this week. McCain said Trump’s controversial comments about immigrants and had "fired up the crazies" at a rally in Phoenix. Trump retorted that the Arizona Republican was "a dummy" who graduated at the bottom of his class at the U.S. Naval Academy.

McCain’s war record was a cornerstone of his 2008 bid for president. A Navy pilot during the Vietnam War, he was captured after his plane was shot down. He was held for more than five years as a prisoner of war.

On Saturday, speaking at a conference of religious conservatives, Trump was pressed on his description of McCain as "a dummy." The moderator, Republican pollster Frank Luntz, described McCain as "a war hero."

"He’s not a war hero," Trump said. "He is a war hero because he was captured. I like people who weren’t captured."

During a news conference after his appearance at the Family Leader Summit, Trump did not apologize but sought to clarify his remarks.

"If a person is captured, they’re a hero as far as I’m concerned. … But you have to do other things also," Trump said. "I don’t like the job John McCain is doing in the Senate because he is not taking care of our veterans."

A spokesman for McCain, Brian Rogers, had no comment when asked about Trump’s remarks.

Trump said he avoided service in the Vietnam War through student and medical deferments. He said he got a medical deferment for a bone spur in a foot, but could not remember which foot. He added that he did not serve because he "was not a big fan of the Vietnam War. I wasn’t a protester, but the Vietnam War was a disaster for our country."

The comments about McCain drew rapid criticism from other 2016 hopefuls. Some have been at the receiving end of Trump insults themselves.

South Carolina Sen. Lindsey Graham, who recently retired from the Air Force, said early state voters in Iowa, New Hampshire and South Carolina would dispense with Trump soon enough.

"Here’s what I think they’re going to say: ‘Donald Trump, you’re fired,’" Graham said, borrowing a line from Trump’s reality television show.

Former Texas Gov. Rick Perry, another veteran, said he was "highly offended by what Donald Trump said about John McCain and his years of sacrifice in a dirty, dingy terrible prison in North Vietnam." He added: "Donald Trump owes every American veteran, and in particular John McCain, an apology."

On Thursday, Trump tweeted that Perry should be "forced to take an IQ test before being allowed to enter the GOP debate."

After Trump’s remarks, former Florida Gov. Jeb Bush tweeted: "Enough with the slanderous attacks. @SenJohnMcCain and all our veterans — particularly POWs have earned our respect and admiration." In the past, Trump has criticized Bush on education and border issues and cracked that "this guy can’t negotiate his way out of a paper bag."

Louisiana Gov. Bobby Jindal and Wisconsin Gov. Scott Walker also condemned the remarks. "You may agree or disagree with some of his politics," Walker said, "but John McCain is an American hero, and I will defend him and any other veteran that’s been a prisoner of war."

Texas Sen. Ted Cruz called McCain an American war hero, but sidestepped when asked whether he would condemn the remarks.

"I recognize that folks in the press love to see Republican on Republican violence," Cruz said. "You want me to say something bad about Donald Trump or bad about John McCain or bad about anyone else and I’m not going to do it."

Former Arkansas Gov. Mike Huckabee called McCain a "great American hero," but he declined to weigh in on Trump’s comments, saying Trump would have to decide whether he wanted to "walk back" his statements.