Every day, a new low. As Britons turned to social networks to try to get credible information about an unfolding terrorist attack in central London on Saturday night, the President of the United States enraged many by injecting himself into the conversation, and trying to turn the wave of anxiety and fear to his political advantage.

Before the nature or scope of the incident was entirely clear even to police officers responding to the rampage, Donald Trump used his personal Twitter account to share unsourced, third-hand speculation about the attack — from an American political blogger — and then lashed out at federal judges for blocking his executive order barring travel from seven Muslim-majority nations as unconstitutional.

A screenshot from Donald Trump’s personal Twitter feed.

After pausing for some rest — and, apparently, to block a musician in Manchester who criticized him for retweeting news “like a bloody ghoul” — Trump resumed his role as Pundit-in-Chief early Sunday morning in Washington, by falsely accusing London’s mayor, Sadiq Khan, of downplaying the attacks as he attempted to instill calm rather than sow panic.

In both a written statement released overnight, and a video message on Sunday morning, Khan urged “all Londoners and visitors to our city to remain calm and vigilant.”

Khan continued to project measured, steely determination during a television interview, when asked what steps the authorities were taking to prevent more “low-intensity attacks,” using vehicles rather than bombs. He replied that “the police and experts and all of us are finding new ways to keep us safe.”

As part of that effort, he said, “Londoners will see an increased police presence today and over the course of the next few days.” There was, the mayor added “no reason to be alarmed” by the sight of those officers.

That message seemed to get through to Londoners, who do indeed take pride in continuing to “keep calm and carry on” when faced with security threats, as reporters for the BBC and Sky News observed.

After Khan’s interview was rebroadcast on Fox News in the United States, however, Trump leapt at the chance to distort the words of London’s first Muslim mayor.

“The mayor is busy working with the police, emergency services and the government to coordinate the response to this horrific and cowardly terrorist attack and provide leadership and reassurance to Londoners and visitors to our city,” Khan’s spokesman told reporters. “He has more important things to do than respond to Donald Trump’s ill-informed tweet that deliberately takes out of context his remarks urging Londoners not to be alarmed when they saw more police — including armed officers — on the streets.”

While Khan refused to take time out to reply to Trump’s tweet, several Britons did, including David Lammy, a member of Parliament running to retain his seat in the general election this Thursday.

Later in the day, the Labour leader Jeremy Corbyn tore into Trump for his attack on Khan.

Senator Chris Murphy, a Connecticut Democrat, also expressed his dismay at Trump’s attempt to whip of hysteria.

Khan, a former member of Parliament for the Labour party, was elected in a landslide last year over a Conservative candidate who spread racially divisive innuendo about the supposed danger of electing a son of Pakistani Muslim immigrants to lead the British capital.

That effort failed badly, however, and the mayor now enjoys an approval rating of 56 percent in polling conducted earlier this week. The same survey also found that more Londoners trust him to keep them safe than trust either the prime minister, Theresa May, or the opposition leader, Jeremy Corbyn.

Despite Khan’s popularity in the city, the mayor’s faith has made him a widely reviled figure in the alt-right communities of online racists Trump’s worldview is marinated in. The president’s main connection to those groups is his former caddy and current social media director, Dan Scavino.

After Khan perhaps disappointed the White House by not replying to Trump’s tweet, Scavino took it upon himself to tweet directly at the mayor of London — who, again, was still dealing with the immediate aftermath of a deadly terrorist attack in his city — to let him know that the president was still angry that Khan said, 13 months ago, “Trump’s ignorant view of Islam could make both our countries less safe” by “alienating mainstream Muslims.”

Trump was also lambasted for another tweet on Sunday, in which he bizarrely implied that since the London attackers used a van and knives to kill, restricting access to guns in the United States would not prevent terrorism.

The new spike in animus for Trump, who was already deeply unpopular in Britain, would seem to make it unlikely that his previously delayed state visit to London will take place any time soon.

The reality that Trump’s presence on British soil would spark massive protests seemed obvious to many in London, but apparently was less understood in Washington, where the president’s aides told reporters that he was considering a visit this week.

The prospect of Trump appearing in the United Kingdom on the eve of a general election delighted those who would like to see Prime Minister May punished for cozying up to the president.