How Donald Trump threw away his very last chance to impress

America can only hope the pattern of Hillary Clinton's political career continues to hold: she's always been better in office than when running for it

Well, that should be it. Game, set and match. The three presidential debates – now mercifully over – have not been kind to Donald Trump, not least the constant use of the split screen which means his peevish, glowering and frequently interrupting persona is permanently on display to viewers.

But the first half hour or so in Las Vegas he seemed to be doing better. He was restrained and on message. He resisted Hillary Clinton’s attempts to bait him. She was on the defensive; he not only sounded like a solid conservative, he sounded presidential too. If not for that damned split screen, he would even have looked it.

Then the familiar Trump took over. A Clinton barb over Putin exploded under that gossamer-thin skin. A promising moment – when she was failing to explain away her dream of open borders across the Americas as expounded in a $225,000 speech to Brazilian bankers in 2013 – simply evaporated.

Instead of pinning his opponent on open borders and immigration, he blundered down the Russia alley, yet again refusing to concede what all 17 US intelligence agencies have concluded and now publicly charged: that Russian hackers are working at the express orders of the Kremlin, in a bid to influence this 2016 US election.

Thereafter it was downhill all the way. In an exchange on experience, Clinton skewered him. Then she nailed Trump-the-protector-of-American-jobs on his use of Chinese steel to build his signature hotel in town. And then Trump, who has spent the past week railing about a “rigged” electoral system, made his biggest mistake, twice refusing to confirm he would accept the result on 8 November. “I will look at it,” he said when pressed by moderator Chris Wallace of Fox News. “I will keep you in suspense.”

Top Republicans couldn’t hide their dismay at this challenge to an underpinning of American democracy; indeed, of democracy anywhere. Even the invited audience gasped, and Clinton pounced.

By the night’s end Trump was reduced to schoolyard abuse. “Such a nasty woman,” he muttered, after Clinton delivered that rarity, an actual joke, this time about Trump’s non-payment of taxes.

In fact, Trump may have performed slightly better than in the first two debates (though an instant poll afterwards had Clinton the winner, by 52-39). But he did nothing to change the trajectory of a race in which he trails substantially, both nationally and in almost every swing state. Once again he doubtless fired up the faithful, but did nothing to win over Republican deserters and whoever at this point is still undecided.

The question now is whether he will drag his hijacked party to defeat in Congress too. A few weeks ago, it seemed Republicans might cling to control of the Senate. Now the Democrats again look poised to make the minimum net gain of four (with vice-president Tim Kaine casting the decisive vote in his role as president of the Senate). And if Trump truly poisons the well, the apparently impregnable Republican majority in the House could also fall. It’s a long shot, but who knows?

Make no mistake, the debate again revealed Clinton’s multiple weaknesses: her staleness, her identification with a discredited and incestuous establishment, her slipperiness, her failure – even at this late point in the day – to come up with a proper theme for her campaign.

America can only hope the pattern of her political career continues to hold. She’s always been better in office than when running for office. May that be true when she enters the White House after an abomination of an election campaign the country just wants to forget.