WASHINGTON -- A Republican Party at war with itself long ago gave up any pretense of everyone getting along. Conservatives-vs.-establishment-GOP battles permeate Washington, and intra-party insults have become so common that they are mostly ignored. In a primary with 17 candidates, it’s about to get much worse.

But shockwaves traveled through the GOP and most of the political arena over the weekend when candidate Donald Trump suggested that Arizona Sen. John McCain wasn’t a war hero in Vietnam just because he was a prisoner of war. “He’s not a war hero,” the real estate mogul said at an event in Iowa on Saturday. “He was a war hero because he was captured. I like people who weren’t captured.”

And if the establishment GOP have their way, that will be the last noteworthy thing Trump says in the 2016 campaign. Sure, most thought his remarks about Mexican immigrants were going to sink his campaign. They didn't, and he actually rose in the polls. But the latest controversy has more Republicans calling foul. 

GettyImages-479775754 Sen.John McCain, R-AZ, speaks during a committee hearing on July 7, 2015 on Capitol Hill in Washington, DC. Photo: AFP/Getty Images/Mandel Ngan

McCain appeared on MSNBC’s “Morning Joe” on Monday morning to respond. But instead of demanding an apology -- which Trump has refused to do -- McCain remained calm (out of character for the normally fiery Arizona senator) and insisted repeatedly that Trump should apologize to the other POWs and the families of those who've died in captivity.

Trump has already demonstrated that he can rally conservatives with remarks that run counter to what the establishment thinks is the way to address voters. When he proposed building a wall between the United States and Mexico and said that Mexican immigrants were criminals and rapists, Washington Republicans quietly stood by while the fallout ensued. They were sure that Trump would implode if they just let him. Instead, Trump skyrocketed to the front of the Republican primary pack -- placing first in several national polls.

Going after McCain -- Trump and he were engaged in a series of barbs that led up to this weekend's remarks -- could have played well for the real estate mogul. McCain has long drawn the ire of conservatives in his own party. He called Sens. Ted Cruz and Rand Paul “wacko birds.” He has been a strong backer of comprehensive immigration reform. He authored a campaign finance law rewrite that limited “soft money.” And he supported “cap and trade” legislation that became the enemy of the tea party movement in 2010.

But Trump’s remarks about McCain -- who spent more than five years as a prisoner in North Vietnam where he was tortured and sustained permanent injuries -- weren’t received with quiet reserve from Republicans just waiting for his campaign to crumble. This time, Republicans pounced.

“Donald Trump didn't just disqualify himself from being president -- he disqualified himself from the privilege of even running for president,” said Tony Fratto, a Republican strategist who is supporting Jeb Bush but isn’t working for any candidates. “Trump isn't fit to serve or even fit to run. Whatever disagreements with John McCain on policy, to flippantly criticize his honorable and heroic military career is unforgivable. His characterization of McCain's service was ignorant and disgraceful. In fact, they were so offensive I do not believe he should be permitted to participate in official debates.”

The Republican National Committee -- which had been quietly fretting about Trump’s immigration remarks -- wasted no time in criticizing his McCain comments. “Senator McCain is an American hero because he served his country and sacrificed more than most can imagine. Period,” said Sean Spicer, the communications director for the RNC. “There is no place in our party or our country for comments that disparage those who have served honorably.”

A Republican strategist who is consulting for a candidate and didn’t want remarks tied to him/her pointed to New Hampshire as potentially carrying big risks for Trump.

“McCain is still well thought of -- New Hampshire rescued his 2008 campaign and propelled him to the nomination -- and vets are very popular there as well,” the strategist said. “He did insult all POWs, and if vets and POW groups that are unaffiliated with Dems come out publicly against him, it'll be a big problem for him.”