The newly elected mayor of London has dismissed an apparent olive branch from Donald Trump, who had congratulated Sadiq Khan on his election to replace Boris Johnson.
Mr Trump has emerged as the surprise Republican Party nominee for the White House, in the November presidential race against the Democrat Hillary Clinton.
He has foolishly proposed a ban on Muslims entering the United States, but said of Mr Khan: “There will always be exceptions.” Mr Khan retorted: “Donald Trump’s ignorant view of Islam could make both of our countries less safe - it risks alienating mainstream Muslims around the world and plays into the hands of extremists.”
One of the many problems with Mr Trump’s unworkable and unpleasant proposed ban is that he has done grave damage to moderate people who are rightly concerned at the alarming rise in Islamic extremism in much of the world, and indeed at the apparent ambivalence of many Muslims about that rise.
There is still no shortage of people who think after the massacres in New York, London, Madrid, Paris and Brussels that the West is somehow to blame for such depravity.
But Mr Khan should be wary about getting on his high horse on this matter. He has been accused of being soft on Islamic extremists. Mr Khan insists that his past actions, such as sharing a platform with a Muslim fanatic, are due to the fact that he was a human rights lawyer.
There has been muddled thinking when it comes to extremism, leading to proposals from mainstream UK politicians such as refusing entry to Mr Trump or the French National Front leader Marine Le Pen. Neither of those two politicians are in the same league as Islamic fanatics who advocate genocide, suicide bombing and brutally repressive social policies.
If, as is possible, Mr Trump reaches the Oval Office, he will be welcome in the UK, one of the US’s closest allies.
Our focus must be on stopping terrorism and exposing those who are ambivalent about it.