Donald Trump might finally have crossed the line.

Appearing on Saturday at the Family Leadership Summit in Ames, Iowa, the real estate mogul took his running feud with Arizona Sen. John McCain to a new level.

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

The remarks, which came after days of back-and-forth between McCain and Trump, were met with scattered boos.

McCain, a former Navy pilot, spent roughly five-and-half years in a notorious North Vietnamese prison known as the “Hanoi Hilton,” where he was repeatedly tortured. He spent two of those years in solitary confinement.

At a press availability following his remarks, Trump denied saying that McCain isn’t a war hero and said, “If somebody’s a prisoner, I consider them a war hero.”

He also continued his attacks on the Arizona senator, saying, “I think John McCain’s done very little for the veterans. I’m very disappointed in John McCain.”

Trump received four student deferments from military service between 1964 and 1968. In Ames, he told reporters another medical deferment he received after graduating was for a bone spur in his foot. When asked which foot, Trump told reporters to look up the records.

In a follow-up statement sent to reporters, Trump again declined to apologize, calling McCain “yet another all talk, no action politician who spends too much time on television and not enough time doing his job.”

Trump’s fellow Republican presidential candidates quickly distanced themselves from his remarks — with a few notable exceptions.

“Enough with the slanderous attacks,” Jeb Bush tweeted. “@SenJohnMcCain and all our veterans - particularly POWs have earned our respect and admiration.”

“John McCain is an American hero. I have nothing but respect for his service to our country,” tweeted Louisiana Gov. Bobby Jindal. “After Donald Trump spends six years in a POW camp, he can weigh in on John McCain’s service,” he added in a second tweet.

”.@SenJohnMcCain is an American hero & all POW’s deserve our nation’s highest debt of gratitude. @realDonaldTrump’s comments are disgraceful,” tweeted former Texas Gov. Rick Perry.

“As a fellow veteran I respect @SenJohnMcCain because he volunteered to serve his country. I cannot say the same about Mr. @realDonaldTrump,” Perry added. He then called in a statement for Trump to drop out of the race.

South Carolina Sen. Lindsey Graham, a close friend of McCain’s, tweeted, “If there was ever any doubt that @realDonaldTrump should not be our commander in chief, this stupid statement should end all doubt.” He added: “At the heart of @realDonaldTrump statement is a lack of respect for those who have served - a disqualifying characteristic to be president.”

At a campaign event in Sioux City, Iowa, Wisconsin Gov. Scott Walker called McCain “an American hero.” At a press gaggle afterwards, he said of Trump, “I unequivocally denounce him.”

“I know @SenJohnMcCain. Senator John McCain is an American hero. Period. Stop,” tweeted New Jersey Gov. Chris Christie.

“America’s POWs deserve much better than to have their service questioned by the offensive rantings of Donald Trump,” tweeted Florida Sen. Marco Rubio, who spoke at the summit before Trump.

Sean Spicer, a spokesman for the Republican National Committee, tweeted: “.@SenJohnMcCain is an American hero because he served his country and sacrificed more than most can imagine. Period.”

“There is no place in our party or our country for comments that disparage those who have served honorably,” he added.

Not all Republicans were ready to condemn Trump. When asked by POLITICO if the mogul’s comments were out of line, Santorum declined to comment. In a tweet, he defended McCain, but did not mention Trump: “.@SenJohnMcCain is an American hero, period.”

Texas Sen. Ted Cruz spoke at length to reporters about McCain’s heroism between signing books and appearing on-stage at the summit, but he, too, declined to condemn the comments when asked about them.

Neurosurgeon Ben Carson, whose appearance followed Trump’s at the summit, declined to comment on Trump’s remarks after leaving the stage. He also would not say when asked whether or not McCain was a war hero. “It depends on your definition of a war hero,” he said.