(CNN) By any conventional standard, Donald Trump just blundered through the worst three days of any presidential candidate in living memory.

Showing a characteristic refusal to back down from a fight, Trump took the almost unthinkable step of publicly escalating a feud with the parents of fallen US solider, Capt. Humayun Khan, who blasted Trump at last week's Democratic convention as unfit for the presidency.

And in an interview with ABC's George Stephanopoulos, Trump said Russian President Vladimir Putin wouldn't make a military move into Ukraine -- even though Putin has already done that by seizing the Crimean Peninsula in 2014.

In any normal political campaign, these stumbles would hobble Trump's ability to pass the fabled commander in chief test, in which Americans take their measure of a candidate and decide whether he is fit to lead them.

But no one needs reminding that 2016 is not a conventional political year.

Trump's previous feuds and torching of political correctness have not doomed him. In some cases, his behavior has lifted him among voters who believe something elemental about their nation is being taken away and who want a candidate who will blow the political system -- and political correctness -- to smithereens.

As if to make that point, Trump was defiant Monday despite a backlash in his own party over his apparently disastrous weekend.

"This story is not about Mr. Khan, who is all over the place doing interviews, but rather RADICAL ISLAMIC TERRORISM and the U.S. Get smart!" Trump tweeted.

"Mr. Khan, who does not know me, viciously attacked me from the stage of the DNC and is now all over T.V. doing the same - Nice!" Trump said as the Khans appeared on CNN's "New Day."

Obama's implicit rebuke

In an implicit rebuke of Trump's comments, President Barack Obama said Monday that "no one has given more for our freedom and our security than our Gold Star families," who have lost loved ones in the line of duty.

Without specifically referencing Trump's comments about the Khan family, Obama said Gold Star families "represent the very best of our country."

"They continue to inspire us every day and every moment," Obama said during remarks to disabled veterans in Atlanta. "They serve as a powerful reminder of the true strength of America."

It could be that the post-campaign chroniclers will identify this weekend as the moment Trump's campaign melted down, never to recover.

After all, a candidate at this stage has to broaden his or her appeal, especially in swing states. In particular, Trump's decision to target the family of a fallen hero appears to have the potential to weigh on the margins of the election in battleground states like North Carolina, Florida and Virginia, where large pockets of military voters and honored veterans are important.

But given that Trump's faithful supporters have never found reason to desert him yet, it seems unlikely that his public showdown with Khizr and Ghazala Khan and a blind spot on Russia policy will cause them to dump him now.

As they showed up for his rally in Columbus, Ohio, Trump supporters did not all feel comfortable with his remarks but none showed any sign of second thoughts about him.

Tom McClanahan said he felt bad for Captain Khan's father, but believed Trump had been set up by the media.

"I think it was just a trap and he kind of fell into it," McClanahan said.

Michael Kawash, from Charleston, West Virginia, said the story was being blown out of proportion by the media.

'He only goes up'

"They're trying to say this is a turning point (at) which his campaign starts to go down. Every time they do that, he only goes up," he said.

Chris Leis, a 36-year-old teacher from Kettering, Ohio, came closest to criticizing Trump, who he said needed a filter because he always has his "mouth running."

But Leis said he would still vote for the billionaire.

"If he just would've thanked the family for their service and for the loss of their life, that would've been better. But it wasn't enough to make me say, 'you know, I don't like this guy and I'm going to go ahead and, you know, vote Hillary'. It's something I couldn't do."

But outside of Trump's loyal supporters, the key question is whether the bulletproof image that Trump maintained during the primary work as well in a general election?

He has again put leaders of his own party in a no win position -- and that could be a problem if it comes to a point later on when they face a decision of whether to cut the nominee loose in a bid to preserve congressional majorities.

Once again they have been forced to choose between rebuking a nominee who destroyed the most talented GOP primary field in a generation and won the votes of millions of Republicans they need to show up in November or of tarnishing their own political brands.

That's why, when House Speaker Paul Ryan and Senate Majority leader Mitch McConnell issued statements on Sunday, they implicitly condemned Trump's comments but did not mention their nominee by name.

Condemnation

It was only as the furor barreled into Monday, with Trump fueling the fire, that the condemnations of Trump became more specific, notably from two party figures who are walking a knife edge in their own re-election races because of the uproar Trump has fanned.

Arizona Sen. John McCain, who had never before taken the bait following Trump's denigration last year of torment as a prisoner of war in Vietnam, issued a long and moving statement.

"In recent days, Donald Trump disparaged a fallen soldier's parents. He has suggested that the likes of their son should not be allowed in the United States — to say nothing of entering its service," McCain wrote. "I cannot emphasize enough how deeply I disagree with Mr. Trump's statement. I hope Americans understand that the remarks do not represent the views of our Republican Party, its officers, or candidates."

"My sons serve today, and I'm proud of them. My youngest served in the war that claimed Captain Khan's life as well as in Afghanistan. I want them to be proud of me. I want to do the right thing by them and their comrades," McCain wrote.

"In the end, I am morally bound to speak only to the things that command my allegiance, and to which I have dedicated my life's work: the Republican Party, and more importantly, the United States of America. I will not refrain from doing my utmost by those lights simply because it may benefit others with whom I disagree."

With those words, McCain seemed to make a case why ultimately Republicans should be ready to lose an election if they see their candidate as antithetical to everything they believe.

Sen. Roy Blunt, who is up for reelection in November, also noted his son's own war service.

"My advice to Donald Trump has been and will continue to be to focus on jobs and national security and stop responding to every criticism whether it's from a grieving family or Hillary Clinton," Blunt said.

Meanwhile, Jeb Bush's top adviser, Sally Bradshaw, has left the Republican Party to become an independent, and says if the presidential race in Florida is close, she'll vote for Hillary Clinton.

She told CNN's Jamie Gangel in an email interview that the GOP is "at a crossroads and have nominated a total narcissist -- a misogynist -- a bigot."

Retired Lt. General Michael Flynn, who supports Trump, said that though he disagreed with him on a lot of things, he agreed that the current controversy was taking away the focus from the main threat to America -- the spread of radical Islam.

He told CNN's Wolf Blitzer he had "no doubt" that the GOP nominee was still prepared to be commander-in-chief, citing his strength, ability to listen to advice when making decisions and his "vision of the direction that this country needs to go."

And Reince Priebus, the Republican National Committee chairman, told Blitzer on "The Situation Room" that it's "up to Donald Trump" to decide whether to apologize to the Khan family.

"Hindsight's 20/20," Priebus said. "But obviously I am who I am, and I'm talking for the party, and I believe these Gold Star families are off limits, and they're to be loved and cherished and honored."

Priebus added: "We don't go there, and I don't go there. Donald Trump is going to speak for Donald Trump. I mean, he wants to defend himself, and it's understandable. But look, like I said before, this is a family that is grieving and they have a right to and we have an obligation to honor them and to love them and to cherish them. That's where I come from; that's where our party comes from."