The Khan controversy may be one insult too many for Teflon Don as his wild campaign shows signs of cracks
Donald Trump has insulted women, Muslims, Mexicans, the disabled and countless other demographics and individuals in this extraordinary, disturbing US election cycle.
Until now, his deeply offensive rhetoric and playground bullying have done little to affect his popularity as his polling numbers continued to rise and he swept to the Republican nomination.
He has even just clashed with the mother of a crying baby in Virginia. Initially, he said: "Don't worry about that baby. I love babies."
But when the baby continued to cry he said: "Actually, I was only kidding. You can get that baby out of here."
It was said with a slight smirk, as laughs and a few gasps escaped from the crowd, and he added: "Don't worry, I think she really believed me that I love having a baby crying while I'm speaking. That's OK. People don't understand. That's OK."
He famously stated he could shoot someone on Fifth Avenue and it would not damage him - and, as the months rolled by, many in America even started to believe that absurd claim.
The question 'has Trump gone too far this time?' has, of course, been posed constantly since the businessman announced he was running in June 2015.
This week, however, in the aftermath of his mockery of the grieving parents of a Muslim American soldier killed in Iraq, it feels like, finally, his luck could be running out and his winning streak coming to an end.
Perhaps it was the horrific realisation, following his formal coronation as the Republican nominee in Cleveland two weeks ago, that Mr Trump is now just one step away from the White House.
Maybe it was the straw that broke the camel's back - the weight of 13 months of often unbelievable insults finally giving way with no sign of the 'presidential' demeanour he had promised to adopt.
Or it could simply have been the fact that Mr Trump was not attacking a political rival or TV personality or journalist or a faceless wider demographic - and that is not to belittle those countless victims.
This time, however, the target in his sights was an ordinary immigrant American family that had suffered the intense grief of losing a child - and he was also a war hero who had made the ultimate sacrifice for his country.
Whatever the reason, the Khan family controversy could be the moment the Trump bandwagon came off the rails.
Barack Obama went for the jugular with his most forceful intervention to date, calling the 70-year-old "woefully unprepared" and "unfit to serve as president".
"He keeps proving it," the US president said, in near disbelief, as he drew a scathing distinction between Mr Trump and past Republican opponents John McCain and Mitt Romney, whom he said he respected and whose ability to lead he did not doubt.
Mr Obama was swiftly backed up by Francois Hollande, the president of France - America's oldest ally - who said he was "sickened" by Mr Trump in an unprecedented intervention from the leader of a Nato ally at this late stage of a presidential campaign.
Mr Hollande went on to say that, if Mr Trump wins in the November election, the very existence of democracy around the world could be under threat.
More significant, though, has been the re-opening of the deep wounds within the Grand Old Party, which were merely papered over in Cleveland.
Leading Republicans Paul Ryan, Mr McCain, Jeb Bush, Mitch McConnell and even Trump ally Chris Christie firmly distanced themselves from their nominee over the controversy.
Richard Hanna, a New York congressman, went one step further, becoming the first elected Republican to say he would be voting for Hillary Clinton in November.
Mr Hanna could be the first of many, as it becomes increasingly impossible for moderate Republicans to contemplate voting for the reality TV star to take over as commander-in-chief.
They now face a moment of reckoning over whether to stand by their unpredictable nominee to the end, or settle for another Clinton in the White House and regroup during the next four years.
Hardcore Trump supporters, who have cheered his lack of political correctness at every twist of the campaign, even sounded a note of caution at a rally in Washington's Virginia suburbs on Tuesday afternoon.
"He could have framed that in a totally different light," Nathan Coryell told reporters in reference to the Khan family controversy.
"I think he needs to apologise," added Chip Galloway, who served in the military for 32 years, stating that Gold Star families who have lost a child in combat should be off-limits - even for Mr Trump.