Just 100 days from the election, Trump has responded in his standard fashion -- dig in, claim he's being treated unfairly and attack back.
But the swift condemnation of Trump's response raises questions about whether this controversy is different from the ones that came before it.
This time, attacks from the Republican presidential nominee on the parents of a soldier who died defending America have put new pressure on GOP leaders to decide whether they will continue to stand by him. Already, the party's leaders in the House and the Senate have distanced themselves from Trump's remarks, and other Republican figures are attacking their nominee forcefully.
"This is going to a place where we've never gone before, to push back against the families of the fallen," Sen. Lindsey Graham, R-South Carolina, said in a statement. "There used to be some things that were sacred in American politics -- that you don't do -- like criticizing the parents of a fallen soldier even if they criticize you."
"If you're going to be leader of the free world, you have to be able to accept criticism. Mr. Trump can't," Graham said. "The problem is, 'unacceptable' doesn't even begin to describe it."
The controversy is over Trump's response to Khizr and Ghazala Khan, whose son was killed in Iraq by a suicide bomber in 2004. The Khans took the stage Thursday night at the Democratic National Convention, where Khizr Khan rejected Trump's proposal to temporarily ban Muslims from entering the United States as unconstitutional, pulling a copy of the Constitution from his breast pocket and saying that Trump has "sacrificed nothing and no one." Trump has since responded by criticizing Ghazala Khan's silence and suggesting she wasn't allowed to speak.
The incident recalls Trump's attack last year on Arizona Sen. John McCain. Trump said at the time that McCain is not a war hero because he was captured and imprisoned in Vietnam. Many had speculated the criticism would spark Trump's decline in the GOP primary race -- it did not.
But there are two key differences: Trump was not yet the GOP nominee and McCain -- himself the 2008 GOP standard-bearer -- is a long-time public figure with experience parrying on the presidential level. The Khans are not.
"This is so incredibly disrespectful of a family that endured the ultimate sacrifice for our country," Jeb Bush, a Trump rival in the 2016 GOP primary, said on Twitter Sunday evening.
"There's only one way to talk about Gold Star parents: with honor and respect," tweeted Ohio Gov. John Kasich, who skipped the GOP convention in his state and has declined to endorse Trump. "Capt. Khan is a hero. Together, we should pray for his family."
Kasich's top strategist in his failed 2016 presidential campaign, John Weaver, tweeted a scathing attack on Trump's handling of the Khan controversy, saying: "Trump's slur against Captain Khan's mother is, even for him, beyond the pale. He has NO redeeming qualities."
Ryan, McConnell weigh in
And both Republican congressional leaders took issue with Trump, issuing statements Sunday that praised the Khan family and reaffirmed their opposition Trump's proposed Muslim travel ban.
"America's greatness is built on the principles of liberty and preserved by the men and women who wear the uniform to defend it," House Speaker Ryan, R-Wisconsin, said. "As I have said on numerous occasions, a religious test for entering our country is not reflective of these fundamental values. I reject it. Many Muslim Americans have served valiantly in our military, and made the ultimate sacrifice. Captain Khan was one such brave example. His sacrifice -- and that of Khizr and Ghazala Khan -- should always be honored. Period."
Senate Majority Leader Mitch McConnell, R-Kentucky, offered similar sentiments.
"Captain Khan was an American hero, and like all Americans I'm grateful for the sacrifices that selfless young men like Captain Khan and their families have made in the war on terror," McConnell said in a statement Sunday.
"All Americans should value the patriotic service of the patriots who volunteer to selflessly defend us in the armed services," McConnell said. "And as I have long made clear, I agree with the (Khans) and families across the country that a travel ban on all members of a religion is simply contrary to American values."
But both men noticeably did not mention Trump by name in their brief statements, that came hours after Khizr Khan called on them to repudiate Trump.
"It is a moral obligation -- history will not forgive them," Khan said of Ryan and McConnell on CNN's "State of the Union." "This election will pass, but history will be written. The lack of moral courage will remain a burden on their souls."
He told CNN's Jim Acosta those GOP leaders have a "moral, ethical obligation to not worry about the votes but repudiate him; withdraw the support. If they do not, I will continue to speak."
Democratic nominee Hillary Clinton also criticized Trump on Sunday, speaking to reporters alongside Democratic vice presidential nominee Tim Kaine, a Virginia senator.
Asked if Trump's attack on the Khan family is a pivotal moment in the election, Clinton said: "Well, he called Mexicans rapists and criminals. He said a federal judge was unqualified because of his Mexican heritage. He has called women pigs. He has mocked a reporter with a disability."
"Ridiculed a POW in John McCain," Kaine interjected.
"That's right," Clinton said. "And any one of those things is so offensive and then to launch an attack as he did on Capt. Khan's mother, a Gold Star mother, who stood there on that stage with her husband honoring the sacrifice of their son and who has in the days since spoken out about the overwhelming emotion that any mother would feel as her son was being honored and then to have Trump do what he did, I don't know where the bounds are. I don't know where the bottom is."
Trump points to soldier's mother
Like the dust-up over Trump's criticism of Indiana-born federal judge Gonzalo Curiel's Mexican heritage, Trump's reaction has been tinged with the stereotyping of Khan's Muslim family.
Trump suggested -- first in an interview with New York Times columnist Maureen Dowd, then in an interview with ABC News' George Stephanopoulos aired Sunday on "This Week" -- that Khan's wife wasn't allowed to speak.
"I'd like to hear his wife say something," Trump told Dowd.
Then, he told Stephanopoulos: "If you look at his wife, she was standing there. She had nothing to say. She probably -- maybe she wasn't allowed to have anything to say. You tell me. But plenty of people have written that. She was extremely quiet. And it looked like she had nothing to say. A lot of people have said that."
Ghazala Khan, Khizr Khan's wife, hit Trump back hard herself in an op-ed in The Washington Post Sunday, saying she declined to speak because she was emotionally distraught -- and suggested Trump lacks empathy if he fails to understand that decision.
"Donald Trump has children whom he loves. Does he really need to wonder why I did not speak?" she wrote.
Trump calls Capt. Khan a 'hero'
Responding to the backlash, Trump issued a statement Saturday praising Capt. Khan as a "hero" and saying the real problem is "radical Islamic terrorists who killed him."
But in that statement, he again criticized the soldier's father.
"While I feel deeply for the loss of his son, Mr. Khan who has never met me, has no right to stand in front of millions of people and claim I have never read the Constitution, (which is false) and say many other inaccurate things," Trump said in the statement.
And Sunday morning, he again weighed in over Twitter.
"Captain Khan, killed 12 years ago, was a hero, but this is about RADICAL ISLAMIC TERROR and the weakness of our "leaders" to eradicate it!" Trump wrote in the first of two tweets.
He followed up later by attempting to shift the focus from Khizr Khan's criticism of his proposed Muslim ban to the Iraq war in which Khan's son was killed.
"I was viciously attacked by Mr. Khan at the Democratic Convention. Am I not allowed to respond? Hillary voted for the Iraq war, not me!" Trump tweeted.
As Trump pushed back, first asking whether Ghazala Khan's silence on stage was related to her faith, Khizr Khan again attacked Trump Sunday on CNN's "State of the Union."
"He is a black soul, and this is totally unfit for the leadership of this country," Khan said. "The love and affection that we have received affirms that our grief -- that our experience in this country has been correct and positive. The world is receiving us like we have never seen. They have seen the blackness of his character, of his soul."
On Sunday night Trump's running mate, Indiana Gov. Mike Pence, issued a statement offering fulsome praise for Humayan Khan as "an American hero." Pence also touted the Trump campaign's immigration plan, which would prevent newcomers from entering the US If they hail from countries "that have been compromised by terrorism."
"Captain Khan gave his life to defend our country in the global war on terror. Due to the disastrous decisions of Barack Obama and Hillary Clinton, a once stable Middle East has now been overrun by ISIS. This must not stand," Pence said.
"By suspending immigration from countries that have been compromised by terrorism, rebuilding our military, defeating ISIS at its source and projecting strength on the global stage, we will reduce the likelihood that other American families will face the enduring heartbreak of the Khan family."
Trump's advisers attempted to move past the controversy, downplaying the direct conflict between Trump and the Khan family.
"What he's saying is that Mr. Trump has a right to defend himself, to make clear what he's saying is this is about Islamic terrorism, for him to be criticized like that he didn't think was fair," Trump aide Jason Miller told CNN's Brian Stelter on "Reliable Sources" Sunday.