Oh dear. After some incendiary comments earlier in the week, Donald Trump has delivered a sucker punch towards Theresa May and her Brexit plan. As the Prime Minister pulled out all the stops for the US President with a black tie dinner at Blenheim Palace, the Sun published its front page – in which Trump declares that May has 'ruined' Brexit and the US/UK deal is off.

https://twitter.com/tnewtondunn/status/1017522456523956224

The US president goes on to add insult to injury by saying May's rival Boris Johnson would make a great Prime Minister. As for that deal, he says:

“ 'If they do a deal like that, we would be dealing with the European Union instead of dealing with the UK, so it will probably kill the deal.'

Trump's bad manners have made Theresa May's bad week even worse. At such a fragile time for her party, the comments will prove even more inflammatory than they are on paper – and they are pretty inflammatory as is. A number of Tory MPs have already taken to Twitter to suggest they agree with Trump – not their leader. Meanwhile Margot James – DCMS minister – has sided with May and tweeted that Boris Johnson would be a terrible Prime Minister.

In trying to sell the Brexit white paper to eurosceptic MPs, No 10 have been insistent that it does not rule out a UK/US trade deal. They say that although there would be a common rule book with the EU on agri food, a deal could be done around this. They also point to the fact that Michael Gove – a Brexiteer – already ruled out bringing chlorinated chicken into the market or undercutting British farmers. However, Trump's dismissal of the Chequers' proposal appears to make the issue black and white: the President of the United States is just not interested in a deal if it involves the kind of caveats May wishes to add.

Yet it's not clear the Brexiteers have enough support for their own alternate plan – or even a plan they can all unite around. Trump has just made Theresa May's fragile position even more fraught. Let's see what today's May Trump Chequers press conference brings.