John McCain isn't a Tea Party darling, but Donald Trump's attack on him could stall the real estate mogul's meteoric rise among conservative Republicans.

Trump's opponents for the 2016 Republican presidential nomination quickly pounced on the reality TV star's assertion that McCain is only a war hero because he got captured. Trump says he prefers servicemen who were not captured.

Former Texas Gov. Rick Perry reacted by issuing a statement calling on Trump to drop out of the presidential race. "His comments have reached a new low in American politics," Perry said. "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."

"Donald Trump should apologize immediately for attacking Senator McCain and all veterans who have protected and served our country," Perry also said in the statement.

"After Donald Trump spends six years in a POW camp, he can weigh in on John McCain's service," Louisiana Gov. Bobby Jindal fired back on Twitter.

Sen. Lindsey Graham, R-S.C., said that if there was ever any question about Trump's lack of qualifications to be commander-in-chief, "this stupid statement should end all doubt."

Trump's statement is obviously not just insulting to McCain personally, but all POWs. While several of the GOP presidential candidates who weighed in most quickly on Trump are still trying to secure a spot on the debate stage in Cleveland next month, the comments could easily trigger a huge backlash against the billionaire among conservative Republican primary voters. Conservative members of Congress are already starting to sound off on social media in defense of McCain against Trump.

Is this the beginning of the end for The Donald? He's never been much for apologizing before–he doesn't even ask God for forgiveness, after all–but he'd be wise to start now.