Republican presidential candidate Donald Trump said Sen. John McCain (R-Ariz.), a decorated Vietnam war veteran, was not a war hero because he was captured by the North Vietnamese. (C-SPAN)

Donald Trump, the celebrity businessman who has rocketed to the front of the Republican presidential race, flippantly belittled Sen. John McCain’s war service here Saturday, inviting a torrent of criticism from party leaders and other candidates.

“He’s not a war hero,” Trump said of McCain at a summit of 3,000 socially conservative activists. He continued, sarcastically, “He’s a war hero because he was captured. I like people that weren’t captured.”

For the past month, Republican leaders have cringed privately at Trump’s inflammatory comments about undocumented immigrants from Mexico and have been aghast at his summer surge to the top of the polls. But they have been reluctant or afraid to condemn a candidate whose outbursts have proven both brash and unpredictable.

That dynamic changed suddenly Saturday. Within an hour of Trump’s slam on the Arizona senator and 2008 GOP presidential nominee, the floodgates opened.

Former Texas governor Rick Perry, himself a subject of recent attacks from the real estate mogul and reality television star, issued a statement saying that Trump was “unfit” to serve as the commander-in-chief and calling on him to “immediately withdraw.”

“As an individual who has worn the uniform of this country, I 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,” Perry said later from the stage in Ames, where 10 candidates addressed the Family Leadership Summit.

Former Florida governor Jeb Bush tweeted, “Enough with the slanderous attacks.” Wisconsin Gov. Scott Walker said Trump should apologize to McCain and “all the other men and women who have worn the uniform” — and then repeated his condemnation Saturday night at the Ames summit. And Sen. Marco Rubio (Fla.) tweeted that prisoners of war “deserve much better than to have their service questioned by the offensive rantings of Donald Trump.” Meanwhile, New Jersey Gov. Chris Christie tweeted, “Senator John McCain is an American Hero. Period. Stop.”

At a state Democratic fundraising dinner in North Little Rock, Ark., on Saturday night, Hillary Rodham Clinton said it was “shameful” that it took Trump’s GOP opponents so long to “stand up to him,” referring mainly to Trump’s statements on immigrants.

“There’s nothing funny about the hate he is spewing at immigrants and their families and now the insults he has directed at a genuine war hero, Sen. John McCain,” she said.

Secretary of State John Kerry, McCain’s former colleague in the Senate, said in a statement that “one thing I know is beyond debate is that John McCain is a hero, a man of grit and guts and character personified. He served and bled and endured unspeakable acts of torture. His captors broke his bones, but they couldn't break his spirit, which is why he refused early release when he had the chance.”

“That's heroism, pure and simple, and it is unimpeachable,” Kerry’s statement said. “If anyone doesn’t know that John McCain is a war hero, it only proves they know nothing about war and even less about heroism.”

But Trump, who has not served in the military and received a series of draft deferments during the Vietnam War, refused to apologize. He later told reporters that McCain — the Senate Armed Services Committee chairman, who oversees the Defense Department, the Navy and Air Force — “doesn’t do anything” in the Senate to help veterans.

After making headlines with controversial remarks about immigrants, 2016 Republican presidential candidate Donald Trump is seeing a surge in the polls. A new Washington Post-ABC News poll finds his favorability increased among Republicans — but is it too early to read into the numbers? (Julie Percha/The Washington Post)

As of late Saturday, McCain had not publicly responded. But at the Iowa event, Sen. Lindsey O. Graham (S.C.) — one of his closest friends, who is running for the GOP nomination — said of Trump: “You’re fired.”

Republican leaders seized an opportunity to disavow what they saw as an outrageous attack against McCain — one of the country’s most distinguished POWs and the recipient of the Silver Star, the country’s third-highest award for valor. They also sought to push Trump from serious contention for the nomination and to relegate his support to the far-right fringe.

Immigration is an explosive issue within the Republican electorate, so party leaders and some other candidates were reticent to directly confront Trump over his calling undocumented Mexicans crossing the border into the United States drug dealers, criminals and rapists. Republicans are concerned that if they can’t make inroads into the Hispanic vote, they will be in serious trouble in national elections.

But GOP leaders are afraid to alienate Trump’s core conservative supporters who staunchly oppose immigration reform, and they worry about angering Trump so much that, if he does not win the GOP nomination, he will pursue an independent run in the general election. Trump again on Saturday said that he would not rule out a third-party run.

But, by belittling McCain, Trump gave more mainstream Republicans an opening to go after him from politically safe ground. Senior Republican strategists said this marked a turning point in the race, with other candidates and the party itself now emboldened to hold Trump accountable for the things he says and believes.

McCain was shot down over North Vietnam in 1967 and suffered a broken leg and two broken arms while ejecting from his fighter jet. He was taken prisoner and received little medical treatment for his wounds, instead enduring almost daily beatings and interrogations by his guards. He lost 50 pounds in 5 1/2 years of captivity and spent much of it in solitary confinement in a windowless room. His injuries remain visible four decades later: He still walks with a slight limp and still cannot raise his arms above his shoulders.

The Republican National Committee, which must stay neutral through the primaries, took the rare step of responding to a candidate’s statement on the campaign trail.

“Senator McCain is an American hero because he served his country and sacrificed more than most can imagine. Period,” Sean Spicer, the RNC’s chief strategist and communications director, said in a statement. “There is no place in our party or our country for comments that disparage those who have served honorably.”

And Mitt Romney, the 2012 nominee who now sees himself as a GOP elder statesman, weighed in by tweeting that the difference between Trump and McCain is that “Trump shot himself down. McCain and American veterans are true heroes.”

Trump fired back on Twitter: “Why would anybody listen to @MittRomney? He lost an election that should have easily been won against Obama. By the way, so did John McCain!”

Veterans leaders also disavowed the comments. “Trump’s asinine comments about Senator McCain’s service are an insult to everyone who has ever worn the uniform — and to all Americans,” said Paul Rieckhoff, founder of Iraq and Afghanistan Veterans of America.

Not every Republican candidate piled on, however. Sen. Ted Cruz (Tex.), who has been perhaps the loudest defender of Trump’s remarks about immigrants and met privately with him a few days ago at Trump Tower in New York, refused to condemn Trump.

Cruz said that he considers McCain “an American war hero,” but that he would not criticize another Republican candidate, including Trump.

“I recognize that folks in the press love to see Republican-on-Republican violence, so you want me to say something bad about Donald Trump or bad about John McCain or bad about anyone else,” Cruz told reporters here. “I’m not going to do it. John McCain is a friend of mine. . . . And Donald Trump is a friend of mine.”

Trump has struck a chord with Republican voters with his direct assault on a political system he decries as corrupt and run by “incompetent people.” From New Hampshire to Arkansas to Nevada, he has promised to rebuild the country. As he said in Ames, “Our country’s going to hell.”

Trump made his “war hero” remark after several days of publicly feuding with McCain. After Trump rallied some 5,000 supporters in Phoenix with an angry, anti-illegal immigration speech, McCain said Trump had “fired up the crazies.”

Trump said he was personally offended by McCain’s reference to his supporters as “crazies” and unleashed a torrent of attacks on the senior senator. Trump tweeted that McCain was a “dummy” for finishing at the bottom of his class at the Naval Academy and called on Arizona conservatives to wage a primary challenge against him when he faces reelection next year.

On Saturday in Ames, Trump said he had once considered McCain a friend — he claimed to have raised $1 million for McCain’s 2008 campaign — but turned on him after he lost.

“He let us down,” Trump said. “I never liked him as much after that because I don’t like losers.”

After exiting the stage, Trump faced reporters for a combative, 18-minute news conference in which he stood by his comments.

Trump said he considers prisoners of war to be heroes — although he called Sgt. Robert “Bowe” Bergdahl, who was held captive in Afghanistan, an exception — but accused McCain of doing little to help veterans in the Senate.

“John McCain talks a lot, but he doesn’t do anything,” Trump said. “I don’t like the job that John McCain is doing in the Senate because he’s not taking care of our veterans. . . . I’m with the veterans all the time. Some of these people wait four or five days just to see a doctor. They sit in a reception room, which is dirty and filthy and disgusting.”

Trump grew hot and agitated by sharp questioning from reporters. Asked if he had read McCain’s accounts of his time in captivity before questioning his war service, Trump replied, “It’s irrelevant.”

Trump added, “I like the people that don’t get captured, and I respect the people that do get captured.” But he would not directly answer questions about McCain. He snapped at one persistent reporter: “Go back to being a pundit.”

Trump did not serve in Vietnam because of several student deferments and a medical deferment. He told reporters that he had a bone spur in his foot, but did not recall which foot had been injured.

“I was not a big fan of the Vietnam War,” Trump said. “I wasn’t a protester, but the Vietnam War was a disaster for our country. What did we get out of the Vietnam War other than death? We got nothing.”

Still, Trump has taken credit on the campaign trail for memorializing veterans.

“I did the Vietnam Veterans memorial in New York,” Trump told voters last week in Laconia, N.H. “You know I was responsible for that.”

T. Rees Shapiro in Washington, Jenna Johnson in Sioux City, Iowa, and Sean Sullivan in Laconia, N.H., contributed to this report.