(CNN)When terror strikes, President Donald Trump tweets.
When an alleged terrorist, one with potential ties to groups like ISIS, carries out an attack, Trump immediately lashes out -- whether or not he has "the facts."
Trump responded to the Friday explosion in the London Underground by 1) declaring that the perpetrator had been "in the sights" of British law enforcement, 2) demanding online recruiting channels be "cut off" then 3) using the incident to push again for a "far larger, tougher and more specific" travel ban.
How Trump would respond to a similar attack inside the US -- one he believes was committed by a Muslim extremist or group -- remains an open and, to many, unnerving question.
"A serious concern is that any demonizing rhetoric would cause people of the same particular demographic as the perpetrator to feel imperiled and less likely to offer assistance," said Tom Sanderson, director of the transnational threats project at the Center for Strategic and International Studies.
But the issue runs deeper. Trump's hair-trigger Twitter finger, now invested with the power of his office, could provoke a dangerous, extralegal response.
"The President's initial rhetoric could likely stimulate some vigilantism," Sanderson said, though he was confident a "more measured follow-on statement" would likely materialize after consultation with senior officials like the attorney general and FBI director.
Still, the Muslim community is on edge. Trump's campaign rhetoric set the tone. His failure to speak out personally after a terror attack on a mosque in Minnesota last month further heightened the tension.
"We don't know what he's going to do. I don't know that he knows what he's going to do," said Ibrahim Hooper, national communications director for the Council on American-Islamic Relations. "He'll use (an attack carried out by a Muslim) to promote his Muslim ban, he'll use it to keep Muslims out of America, he'll use it to make it harder for American Muslims to do anything -- he proposed shutting down the Internet today."
Trump's unique ability to deliver his message, unedited and unvetted, via Twitter and other social media, along with his stated disdain for the constitutional constraints on his authority, typically imposed by the courts, creates the potential for crisis in the aftermath of an attack.
One fear is that some form of the chaos that followed his first travel ban order could be revived. In that case, the Department of Homeland Security was left scrambling to interpret the order only after Trump signed it. According to court filings, one Border Patrol agent referred questions to the President himself.
The White House has since tidied up its operation. The man running then running the DHS is now Trump's chief of staff. But even if retired Gen. John Kelly can slow or prevent a rash executive action, he is unlikely to seize Trump's (mega)phone.
On Friday, UK Prime Minister Theresa May scolded the President over his Scotland Yard tweet, saying it is "never helpful for anyone to speculate on what is an ongoing investigation." But Trump doesn't so much "speculate" as make outright, often unfounded accusations.
But it's Trump's criticism of London Mayor Sadiq Khan that provides the best -- and perhaps the most troubling -- preview of how he would handle an attack similar to those carried out recently in the British capital.
When Khan urged calm, asking Londoners to take the increased police presence in stride after the deadly London Bridge incident back in June, Trump had a fit.
"At least 7 dead and 48 wounded in terror attack," he tweeted, "and Mayor of London says there is 'no reason to be alarmed!'" White House social media director Dan Scavino followed suit, ridiculing Khan and bellowing at him to "WAKE UP!!!!"
No one is quite sure what Trump would do if confronted with the same set of circumstances on American soil. But given his criticism of officials in London, who have urged calm at every turn, it's hard to imagine he would follow their lead.