America's greatest ally suffered another terrorist attack Saturday night at the London Bridge. Seven people are dead and dozens injured after being stabbed or run over at 50 miles an hour.

President Trump took this as an opportunity to vent his spleen via Twitter, railing against gun control, pushing his judicially-blocked travel ban and, most oddly, attacking the Mayor of London.

Here is the offending statement from the Mayor of London: “Londoners will see an increased police presence today and over the course of the next few days. There's no reason to be alarmed.”

This seems utterly unobjectionable. Expressions of increased vigilance and the resolve to live free from fear are what leaders do when confronted with domestic terror, following a model set by Winston Churchill during the Battle of Britain: Keep Calm and Carry On.

So why would the mayor of London be singled out for a Trump twitter attack while his city prepares to bury the dead? It seems petty, cruel, and stupid—blaming the victim and undercutting our allies in a moment of maximum pain and peril.

The answer can't be politics. It's unlikely that Donald Trump has deep feelings about the Conservative versus Labour versus Lib-Dem contest, though he should know that America's closest ally is 5 days away from a general election.

Donald Trump's dislike of Mayor Khan can't even be credibly described as personal. He's never met the man.

The fact that the mayor of London, Sadiq Khan, is Muslim just might help explain the President's animus. Dig a little deeper and you can see not only the baseless accusation of weak leadership but also intimation of divided loyalty. This is fear-fueled xenophobia dressed up as tough-minded real talk.

Does the western world have a problem with terrorism? Yes. We're confronting an apocalyptic death cult that uses Islam as an excuse to wage war on civilians.

But another great trend of our time is the ethno-nationalist pushback to globalization fueled by fear of immigration and compounded by economic and cultural anxiety.

The irony is that immigration, consistent with assimilation, makes the western world economically and culturally stronger—while delivering the ultimate rebuke to terrorists’ ideology.

Sadiq Khan’s faith, while incidental to doing the job of mayor, should be understood as a source of strength in the wider war against terrorism. It sends exactly the message great cities in the West ought to send to the world: as long as you are willing to work hard and play by the rules, we want you here. This is not only a sign of economic and cultural confidence—it's ultimately a recognition that pluralism is the best answer to extremism.

That the presence of a Muslim mayor has not inoculated London against terror attacks is not at all surprising. Terrorists target civilians for reasons unrelated to who is running our respective governments – which is why mushy minded, ‘let’s talk it all out’ responses are naïve. Terrorists are threatened by freedom, democracy and diversity and that is why we must unflinchingly fight them to the death, when necessary.

But feeding into broad narratives about Islam versus the West makes our job of winning this long war much harder. Unintentionally echoing terrorist talking points about an irredeemable clash of civilizations ends up perpetuating the illusion of moral equivalence terrorists push to new recruits.

Mayor Khan represents an example of equal opportunity based in individual achievement that terrorist propaganda can't easily dismiss. The “us against them” script is harder to impose on society. Unfortunately, our president is drawn to divisive comments that debase the office. Attacking the mayor of a suffering city is just the latest example of President Trump alienating our allies while emboldening our enemies.