This is different because it is more direct. It is a direct challenge to Britain and its values. May could not avoid commenting on Trump’s retweeting of the Britain First videos while at the same time credibly maintaining her own genuine commitment to anti-racism. But now the argument has also become personal. For an American president to address a British prime minister in this manner and on such a subject is without any modern precedent. It draws a line about values. May and Trump are on different sides of it. Trump is not May’s friend, Britain’s friend or a friend of the values that this part of the world stands for and must uphold.

Britain should ask for an apology. In a rare – much too rare – intervention in UK politics on Thursday, David Miliband called Trump’s tweets “dangerous, irresponsible, hateful, jaw-dropping, offensive to everything we should stand for” and suggested an apology was due. And so it is. May should reprimand Trump publicly and on the record.

The tweets also make a Trump state visit to Britain inconceivable, now or at any other time. The original invitation was wholly premature and inappropriate.