The prime minister, who is expected to meet Donald Trump later this week, will find her task of dealing with him as tricky as trying to pin jelly to a wall.
For I doubt whether a more fickle and scary President has ever entered the White House.
For instance, he was saying during the campaign that Hillary Clinton should be in jail. Yet at the inauguration lunch, he had nothing but warm words for her.
And again, during the campaign, he bitterly attacked America’s secret services. Yet last weekend he was praising them to the skies.
What is more, he has accused the media of lying (and warned ominously they will have a big price to pay) for claiming that the crowds at his inauguration were far smaller than those at Obama’s in 2009.
Yet it was plain to see the huge empty spaces at the Trump event, compared to the selfsame jam-packed areas during his predecessor’s inauguration.
At the moment, Trump is making all sorts of pro-British remarks, applauding Brexit and looking forward to trade deals advantageous to both the US and the UK.
But given his erratic record, who can be sure that he won’t suddenly change his mind and decide that Britain is not so wonderful after all? He has shown that what he says one minute can be turned on its head the next.
Theresa May has also vowed to express her dislike to him of his anti-women comments, which will no doubt enrage this volatile man.
So, to purloin the expression so often used by the early 20th century British Prime Minister, Herbert (“Squiffy”) Asquith, we shall just have to “wait and see”. But the outlook is not promising.
• Jeremy Corbyn may well be justified in quivering in his boots at the prospect of two critical by-elections next month, Copeland and Stoke-on-Trent Central, both of them Labour-held seats.
But for how much longer? Speculation, which appears to be firmly biased, is suggesting Labour could lose both seats on February 23, an event that would deal not only a devastating blow to Corbyn’s leadership, but worse still, would question the ability of Labour ever to aspire to being a governing party again.
The decision of Labour MPs Tristram Hunt (Stoke Central) and Jamie Reed (Copeland) to quit Westminster and seek lucrative jobs outside Parliament, could well be attributed to their distaste at being led by a hard-line left-winger like Mr Corbyn and their fears of remaining in Opposition for years to come - a highly dispiriting scenario.
Lord Mandelson claims there are more Labour MPs who will follow these two out of Parliament. If such a thing happens it would spell doom for Corbyn’s leadership, and even those people outside Parliament who voted him in as leader by a substantial majority, might be thinking again.
You can tell by merely watching and listening to the lukewarm reaction of many Labour MPs to Corbyn’s efforts to impress in Parliament, notably at Prime Minister’s question time.
Corbyn is a protester and not a political leader. Perhaps those who support him will at last cotton on to that if these by-elections spell disaster for Labour, as well they might.
• Theresa May’s forthcoming appearance on the cover of American Vogue is reminiscent of Margaret Thatcher, an equally snappy dresser and an avid reader of upmarket high-fashion journals like Vogue and Harper’s Bazaar.
Once I was waiting in the entrance hall of No 10 to pick up a document when Mrs Thatcher came down the stairs, bearing copies of Vogue and Harper’s Bazaar. She was going to Chequers.
An attendant pointed out to her that a TV crew was waiting outside. And Mrs Thatcher did not like people to think she had enough time on her hands to read women’s magazines. So she snatched a copy of the Financial Times from under her husband Denis’ arm, and wrapped it round the magazines.
She then whispered in my ear: “You didn’t see that, did you? You didn’t see anything...”
Then she sailed out brandishing her rather inflated copy of the Financial Times in front of the cameras.
• Russian prostitutes are the best in the world, claims Vladimir Putin.
How does he know?