In the aftermath of the London attacks, that city's mayor, Sadiq Khan, is taking heat from American conservatives.

Their gripe?

Khan's call on Britons to stay ''calm and vigilant''.

They suggest that Khan is delusional to the threat his city faces and to the need for improved security.

But I think Khan's critics are confused. This is a case of transatlantic lost-in-translation.

In the United States, a politician who tells citizens to ''keep calm'' in the aftermath of a terrorist attack would be regarded as delusional. Even robotic. Americans like our leaders to speak emotionally and aggressively.

That's not the case in Britain.

There, the notion of keeping calm is a deeply embedded social concern. It's also a point of deep pride.

The roots of this pride reach back to the Nazi bombing raids on Britain from 1940-1941. Those attacks smashed British cities, killing tens of thousands of British civilians and turning entire blocks to dust. But they also produced a powerful psychological effect. Rising from their shelters the morning after each attack, and gazing on the still burning fires, they must have been tempted to despair. After all, the bombing was believed to be a precursor to a final German invasion.

But what what sustained Londoners through the storm was a sense of moral purpose. That whatever happened, they would remain steadfast and never surrender to fear or to tyranny. That they would embody stoicism and courage until the end. Whatever that end might be. In a speech to the British Parliament, President Reagan once offered an anecdote recognizing this British character trait. The line played very well. Reagan, unlike Trump, always knew the right line for the right audience.

Albeit subtly, this tradition is what Sadiq Khan is referencing. He is not telling Londoners that the attacks are insignificant. He is simply telling them to keep going.

But let's turn this issue on its head for a second.

Because each time I watch other American conservatives attack Khan as delusional, I wonder what it says about them. From my perspective, there's a pathetic quality to someone who wants their leader to tell them to panic. A leader should be resolute, and determined. He or she should not wail from the rooftops. In situations such as this, where doubt is the natural impulse of a scared populace, confidence from leadership is priceless. Hyperbolic early morning tweets do not engender confidence in command.

This isn't to say that the U.K. doesn't need changes to its counter-terrorism strategy. It does. Yet we should think more carefully before criticizing Khan. He is leading his city in a difficult moment. And he is rightly deferring counter-terrorism operations to the prime minister, Theresa May.