And of course, they have to get along, at least when it comes to appearances. These countries are allies, and although the president’s conduct during the election campaign left many in the UK angry, he is now in office, and cannot be ignored. The UK and US have shared responsibilities in many areas, and Mrs May has to find whatever common ground is available, and build on it.
As the Prime Minister said, there will be areas where the two do not agree, but in the best traditions of diplomacy, she stressed that there is more that unites the two countries than divides them.
It is too easy to criticise Mrs May for laughing at Mr Trump’s attempts at humour, or for failing to take him to task on issues such as immigration, or for sounding too enthusiastic when she described his election victory as “stunning”. There is nothing to be gained from alienating her counterpart at this stage, and like it or not, she has to work with him.
We should also consider that Mrs May is the first world leader to meet the new president since his inauguration. That does not mean she should feel gratitude, but it suggests that if she needs to address him, he appears willing to listen. A line of communication is open.
None of this should be mistaken as approval for Mr Trump. It is simply the language of diplomacy.
The press conference did not shed much light on the biggest issues, and talks were expected to take place later on Syria and Russia. There was not a great deal of substance to what we learned, and even on Nato, an assurance from Mrs May that Mr Trump is 100 per cent behind the alliance was unconvincing. These were her words, and although she attributed them to her counterpart, he did not verbally endorse her claim when he had the opportunity. His most recent statement on this subject remains that he considers Nato to be obsolete.
Of course, we are not party to the talks that were later to take place on Russia and Syria, which could have resulted in difficult disagreement. But the most concerning aspect of the press conference was when Mr Trump was challenged on torture.
“I happen to feel it works,” said Mr Trump with reference to waterboarding, a practice which appalls many in the UK and elsewhere.
He indicated that he will default to defence secretary James Mattis on this subject – yet how many of us believe that Donald Trump defers to anyone?
Mrs May should be satisfied with her first encounter with Mr Trump. There will be harder times ahead, and she may well have more work to do on Nato. But to deal with the challenges that are sure to follow, she needed to establish a working relationship. On that front, she appears to have made what could be valuable progress.