Maybe it was the warm embrace of the pale blue comfy sofa in ITV’s This Morning studio. Maybe it was the good cheer provided by the twin peaks of the baubled Christmas trees in the background and the festive decorations on the glass table in front of him.

The previous week, Jeremy Corbyn had resisted all attempts by the BBC’s Andrew Neil to apologise for antisemitism in the Labour party. Time and again the Grand Inquisitor had tried to get him to say sorry, but his SAS training in resisting interrogation techniques had proved invaluable.

But the Labour leader was putty in the hands of Phillip Schofield and Holly Willoughby. Well, maybe not quite putty but certainly more of a pushover. Initially Corbyn had several times avoided saying the ‘S’ word, preferring instead to talk about all the processes he had instituted within the party to deal with anti-semitism and how he wanted everyone to feel secure.

“Just say sorry,” Bad Cop Phillip pleaded.

And eventually Corbyn cracked, saying that obviously he was very sorry. Quite why it had taken him so long was something of a mystery; not least as he had already said sorry several times in the past. Most politicians have no problem with repeating themselves – often in the same sentence – but with apologies the Labour leader is happy to make an exception. Sorry is a word to be used sparingly, even when to say it would save himself a whole load of grief.

Sensing the apology might have taken it out of him a bit, Good Cop Holly enquired if maybe Corbyn was exhausted by the election. God knows, the rest of the country is. It’s hard to remember a more toxic and depressing campaign, one dominated by negativity and a refusal by the prime minister to either engage with the public or the truth. Corbyn insisted he was fresh as a daisy.

“Are you sure you’re not exhausted?” Good Cop asked again.

No he definitely wasn’t. Corbyn was having the time of his life, even if everyone else was experiencing the nightmare of theirs. And he would happily be carrying on as Labour leader for the next five years regardless of what happened next week. As for the immediate future, he would be putting up his own Christmas tree on 12 December and keeping a record of what a wonderful time he had had on the This Morning sofa.

Good Cop Holly enquired if maybe Corbyn was exhausted by the election. God knows, the rest of the country is

To be fair, Corbyn did look as if he had enjoyed the interview, in as much as he ever appears to enjoy anything. Deep down, he’s a bit of a miserablist. Something I quite understand and respect. It’s generally good to start with the premise that there’s no bad situation that can’t be made worse. Though in this instance, the Labour leader must have been slightly disorientated because – along with the apology – he had come out of the exchanges well ahead.

Bad Cop had opened by bringing up Johnson’s rant in the Sun about Corbyn being a threat to national security, which Corbyn had politely rebutted by observing that it had been the Tories that had introduced wholesale cuts to the police, the courts, the probation service and countless rehabilitation programmes and that Labour was committed to remaining a member of Nato. You can’t get much more mainstream than that.

Morning TV was not the time to deal with the metaphysics of the US president’s capacity for rational thought, so the Labour leader sidestepped the issue of Donald Trump having said he had never thought of buying parts of the NHS even though he was on record as having had just that thought. Instead he chose to point out the absurdity of Conservative recent suggestions that the ‘NHS for sale’ dossier was a KGB plant. Reminder: it was the Tories who had uploaded the documents to the internet and they have never denied their authenticity. And it is the Tories who have refused to publish a report into interference in British elections.

Clearly the arrival of the US president for the Nato conference has sent Conservative campaign headquarters into something of a tail spin. Which could explain why Johnson was sent 100 miles out of London to Salisbury in Wiltshire on a totally pointless visit to a safe Conservative seat. Having had to borrow £10 off an aide to buy a brownie – he never carries cash in case one of his children tries to rinse him, – he inadvertently posed in front of a “Simply Nuts” sign and been ticked off by a veteran for having let himself go, the prime minister went into overdrive.

Rowena Mason (@rowenamason) Perhaps unwisely Boris Johnson now in front of a “Simply Nuts” sign pic.twitter.com/ADQzYgdtoy

Boris had never heard of Donald Trump, let alone met him. Donald who? What? He was the US president? And he was in the UK? Fancy that. And he was obviously telling the truth because otherwise he would never have made such an effort to put some distance between them. He didn’t even know the US was in Nato. Couldn’t we talk about Emmanuel Macron and Angela Merkel instead.

It was all a bit desperate. Trump had already damaged the Tory campaign earlier that day by saying he wasn’t going to interfere in the UK elections, only to follow up by declaring he was backing Boris and Brexit. The Orange Sun God has yet to claim a brain cell. Johnson groaned. It was just his luck that the one person who could seriously derail an election victory was the leader who was an even bigger liar than himself.

John Crace’s new book, Decline and Fail: Read in Case of Political Apocalypse, is published by Guardian Faber. To order a copy go to guardianbookshop.com or call 0330 333 6846. Free UK p&p over £15, online orders only. Phone orders min. p&p of £1.99.