The president stomped on the White House's message.
Trump had mocked Sadiq Khans response to the latest terror attack in the British capital.
WHAT'S HAPPENING
Mayor Sadiq Khan "has more important things to do than respond to Donald Trump's ill-informed tweet."
J.K Rowling and Christiane Amanpour are among those setting the record straight.
"The Trumps and their supporters have embraced this crazy myth that you can completely eradicate terrorism."
At least four are dead in London after a terrorist drove through pedestrians on Westminster Bridge, before stabbing a police officer outside the Houses of Parliament.
The world saw a wave of protests one day after Donald Trump became president of the United States.
Sadiq Khan could be banned from the U.S. if Trump follows through on his promises.