On the evening of June 3, three ISIS-inspired terrorists rammed their van into pedestrians on London Bridge before getting out and stabbing people in bars in London's nearby Borough Market neighborhood, killing seven people and wounding 48.
The next morning, the city's popular Muslim mayor, Sadiq Khan, went on television to encourage Londoners to stand strong in the face of terror and not to be frightened by the increased police presence in the coming days.
"We will never let them win, nor cower in fear," Khan said. "Londoners will see an increased police presence today and over the course of the next few days. There's no reason to be alarmed."
Khan's comments enraged Trump, who promptly took to Twitter to blast the mayor.
As Vox's Zack Beauchamp explained, Trump took Khan's comments completely out of context: The mayor was saying there was no reason to be alarmed by the increased police presence in the area, not by terrorism in general.
At first, Khan didn't respond to Trump directly, choosing instead to have a spokesperson slam Trump in a statement to the press. "[The mayor] has more important things to do than respond to Donald Trump's ill-informed tweet that deliberately takes out of context his remarks," the spokesperson said.
This seemed to only incense Trump further. The next day, the president again attacked the mayor on Twitter:
Khan finally weighed in later that day on television, telling the BBC: "Some people thrive on feud and division. We are not going to let Donald Trump divide our communities."
Remember: This is a man whose city had suffered a devastating terror attack just two days before and who was trying to help the people of London recover. And the president of the United States was picking a fight with him on Twitter for absolutely no reason whatsoever.