Editor's note: This story has been updated with additional comment.
Former Gov. Rick Perry, who has seized the mantle as the most vocal Republican critic of Donald Trump's presidential candidacy, upped the ante Saturday by calling for the bombastic billionaire to immediately exit the 2016 race.
Perry's statement came shortly after Trump, speaking in early-voting Iowa, called into question whether U.S. Sen. John McCain, R-Ariz., was a true war hero. McCain, a former Navy pilot, was imprisoned and tortured for several years after his plane was shot down during the Vietnam War.
"He's a war hero because he was captured. I like people that weren't captured," Trump said.
"Perhaps he's a war hero, but right now, he's said bad things about a lot of people," Trump added.
Shortly after Trump left the stage, Perry pounced on the remarks.
Trump's "comments have reached a new low in American politics," Perry said in a statement. "His attack on veterans make him unfit to be Commander-in-Chief of the U.S. Armed Forces, and he should immediately withdraw from the race for President."
Perry did not let up Saturday evening speaking from the same stage where the billionaire made the controversial remarks, the Family Leadership Summit in Ames. In an exchange with moderator Frank Luntz, Perry lit into Trump unprompted, calling his comments "as disturbing to me as I’ve heard in this entire process of running for the presidency of the Untied States" and saying that Trump "doesn’t understand or doesn’t care about people who serve this country."
"As an individual who has worn the uniform of this country, I was highly offended what Donald Trump said about John McCain and his years of sacrifice in a dirty, dingy, terrible prison in North Vietnam," Perry told Luntz.
"Donald Trump owes every American veteran and, in particular, John McCain an apology," Perry added.
Perry's overall reaction was the swiftest and sharpest of any presidential candidate Saturday. And it fit in with Perry's efforts to prioritize the military vote as a veteran himself who spent five years in the Air Force.
The former governor has already taken on Trump over his remarks last month generalizing people in the country illegally as criminals. Trump has refused to back away from those comments, despite varying degrees of condemnation from Perry and other GOP hopefuls.
The other Texas Republican in the race, U.S. Sen. Ted Cruz, has been a rare exception, refusing to directly criticize Trump for his remarks on illegal immigration. Reacting to the McCain comments Saturday afternoon, Cruz again avoided a confrontation with Trump.
"John McCain is an American hero," the senator tweeted. "Although we have some policy disagreements, I'm proud to serve alongside him."
In a statement released as the backlash grew, Trump showed no inclination to back away from his comments about McCain.
"I am not a fan John McCain because he has done so little for our Veterans and he should know better than anybody what the Veterans need, especially in regards to the VA. He is yet another all talk, no action politician who spends too much time on television and not enough time doing his job and helping the Vets," Trump's statement said.
"I have great respect for all those who serve in our military including those that weren't captured and are also heroes," the statement added.
A Trump spokeswoman did not immediately respond to a request for comment on Perry's call for the businessman to drop out of the contest.
Abby Livingston contributed to this report.