Read more: Trump breaks royal protocol within seconds of stepping off helicopter
After an appalling two weeks, Keir Starmer needs this kind of stupid intervention like a hole in the head. Yes, Starmer has flip-flopped on Trump, as he has on just about everything.
Starmer once described Trump's views as "repugnant" and said: "An endorsement from Donald Trump tells you everything you need to know about what is wrong with Boris Johnson's politics and why he isn't fit to be prime minister."
But even Starmer now recognises that, whoever's in the White House, Britain's interests are served by a bit of pomp, pageantry and flattery, while welcoming the President with open arms.
Does that mean rolling over and agreeing with everything Trump says and does? Of course not. There's plenty we can disagree with, like tariffs, Ukraine and Greenland, and we can put our views forcefully. But we can also do so civilly and respectfully and in a way that's consistent with the special relationship.
But Khan sees none of that. Having said that Trump's first state visit six years ago should be cancelled and that the UK should not welcome him, Khan has now doubled down on that playground sentiment, saying that Trump's policies are "straight out of the autocrat's playbook" and that "we must also tell President Trump and his supporters to stop talking down and denigrating our great capital city."
Does he really think Trump will listen to a guy who moans and squeals like that? Does he really think it helpful to throw schoolboy insults at the world's most powerful man - everything from 'racist' and 'sexist' to 'homophobe'?
In a spat between Trump and Khan, there will only ever be one winner. And if Khan wants to boast about London's free speech, he could choose a better time than just a week or so after five policemen arrested Graham Linehan at Heathrow for a joke on social media.
Khan purports to speak for everyone in London. But it is not his place to say whom the great city should welcome. Britain's capital is for all of us, and on a day like this it must represent the whole country. Khan may be London Mayor. But London is not his city. He is letting Londoners down, and Britons as a whole, with his silly antics.