Donald Trump cannot lose, will not lose, will never be a loser, but he knows he is headed for defeat. "I'm afraid the election is going to be rigged, I have to be honest,” he told a crowd in Columbus, Ohio. On Fox News, he went further. "I hope the Republicans are watching closely or it’s going to be taken away from us,” he said. “People are going to walk in, they are going to vote ten times maybe. Who knows?”

Trump can no longer brag about the latest polls at his rallies. This dangerous, irresponsible riff fills the gap. In the last seven major surveys, he trails Hillary Clinton by an average of seven points. The Democrat’s post-convention ‘bounce’ has more than wiped out his own.

If Trump does lose, Khizr Khan’s speech at the Democratic National Convention will be remembered as the turning point. Standing in front of a giant portrait of his son, Captain Humayun Khan, who was killed by a car bomb in Iraq, the Pakistani-American lawyer pulled a copy of the US Constitution from his jacket pocket and asked if Trump had ever read it.

“Have you ever been to Arlington cemetery? Go look at the graves of brave patriots who died defending the United States of America,” he continued. “You will see all faiths, genders, and ethnicities. You have sacrificed nothing - and no one.”

It was great theatre, a moment replayed over and over on cable news, but absent Trump’s typically intemperate response, it would have been forgotten about in a day or two. By hitting back, the Republican nominee prolonged the furore for a week and exposed a campaign in meltdown.

He started by attacking Ghazala Khan on ABC News. “His wife, if you look at his wife, she was standing there. She had nothing to say,” he told George Stephanopoulos. “Maybe she wasn’t allowed to have anything to say.”

From there, he took it to Twitter, his preferred venue for settling scores. “I was viciously attacked by Mr. Khan at the Democratic Convention,” he wrote. “Am I not allowed to respond? Hillary voted for the Iraq war, not me!”

On an Ohio radio station, WSYX, he clumsily implied that Khan, who is a Muslim, is a terrorist sympathiser. “When you have radical Islamic terrorists probably all over the place, we’re allowing them to come in by the thousands and thousands and I think that’s what bothered Mr. Khan more than anything else,” he said.

Start the right wing smear machine. Roger Stone, a confidant of Trump’s and the business partner of campaign manager Paul Manafort, accused Khan of being a “Muslim Brotherhood agent helping Hillary” based on the fact that he wrote a dissertation titled Juristic Classification of Islamic Law while living in Saudi Arabia in the 1980s.

In his speech and subsequent interviews, Khan singled out Republican legislators Paul Ryan, the Speaker of the House of Representatives, and Mitch McConnell, the Senate Majority Leader. “Isn’t this time to repudiate Trump?” he asked them. “There comes a time in the history of a nation where an ethical, moral stand has to be taken regardless of the political costs.”

Both men were emphatic in their defence of Khan, but neither withdrew their endorsement of Trump. “I cannot emphasise enough how deeply I disagree with Mr. Trump's statement,” wrote Senator John McCain, but he could not bring himself to jump off the train.

Other than the Never Trump Republicans who declared their opposition during the primaries, the upper echelons of the party have remained remarkably steadfast. Billionaire donor Meg Whitman endorsed Hillary Clinton this week. Congressman Richard Hanna called Trump “a national embarrassment,” but of the thirty-four Republican Senators up for re-election in November, only Mark Kirk of Illinois has repudiated the party’s nominee.

A group of seventeen Gold Star families - parents of children killed while serving in the United States military - released a statement calling Trump’s comments about the Khans “repugnant, and personally offensive to us.”

Trump does not do repentant, but even by his standards, it took some nerve to display a Purple Heart, given to him by a supporter, at his next rally. The medal is issued to soldiers wounded or killed while serving in the armed forces. Trump got five deferments from the Vietnam draft, the last for bone spurs on his heel. “I always wanted to get the Purple Heart. This was much easier,” he tweeted.

Clinton’s campaign is pressing its advantage with adverts impugning Trump’s character. The latest shows children watching Trump on television as he suggests protesters should be beaten up, claims Fox host Megyn Kelly has “blood coming out of her wherever,” and mocks disabled New York Times reporter Serge Kovaleski.

There are still three months to go until the election. Trump could perform unexpectedly well in the debates. But he needs to turn things around soon. Polls taken six weeks after the conventions almost always predict the winner. On Wednesday it was reported that Republican National Committee head Reince Priebus, former New York City mayor Rudy Giuliani and former House Speaker Newt Gingrich were planning an “intervention” to convince him to change his tone.

The following day, Fox News - for all the disputes with Kelly and outgoing CEO Roger Ailes, still Trump’s most reliable cheerleader - released its latest survey. Trump trailed Clinton by ten points. 72% of respondents said she has the knowledge to be President: 40% said Trump does. 64% said she has the temperament: 37% said the same about him.

More than two-thirds of the people polled, including a majority of Republicans, said Trump’s comments about the Khan family were “out of bounds.” There are many reasons that he should not and will not be President, but his inability to walk away from a fight, no matter how small, is high on the list. As Clinton put it this week, reprising a line from her convention speech: “Anyone who can be provoked by a tweet shouldn’t be anywhere near nuclear weapons.”