This isn’t complicated. The purpose of terrorism is to terrify people. Terrorists want masses of people to respond irrationally and live in fear. That is how they draw their power. That is their goal. But Britons will have none of it. They keep calm and carry on. Trump doesn’t like that.
Of course, Trump didn’t criticize the mayors of Orlando, San Bernardino, Baltimore or Portland for trying to calm their people. Of course, he also hasn’t once mentioned the terrorist attacks in Baltimore and Portland. But what could it be about Sadiq Khan that makes Trump need to lash out? Why a personal swipe at Sadiq Khan? What could it be?
But the worst of it is that Trump wants people to be afraid. His initial tweets, even before he expressed sympathy, were to use the London attacks to pursue his own agenda. Then he goes out of context to criticize London’s mayor for urging calm. Trump objects to people trying to respond with purposeful calm. Think about that. The terrorists want people to be terrified. Trump seems to agree.