It's not clear whether Trump's off-the-cuff comments were meant to be a reiteration of his past calls to ban Muslims from entering the United States or if it's a new, more expansive call to curtail all travel in and out of the country. The closest thing to the latter we've seen in recent history was the grounding of flights after 9/11 — a temporary measure narrowly focused on the precise type of threat that had been presented. Beyond that, and beyond laws in the early 20th Century limiting particular types of immigration, we've never seen an incident in which the country halted all migratory traffic. (Which, of course, would be a logistical challenge of enormous scale.)
Trump's past comments on closing the border to Muslims met with a receptive audience from the public. National polling in the wake of Trump's proposal showed support from members of his party for the idea. When the question has been asked in exit polling from Republican primaries, huge majorities expressed their support for the idea — and pluralities of that group expressed their support for Trump in every state except Ted Cruz's home of Texas.
The attacks in Belgium came less than 24 hours after Trump outlined another way in which he hoped to contract America's presence in the world. In an interview with the editorial board of The Post, he expressed skepticism about the U.S.'s role in NATO, the international military alliance headquartered in Brussels.
"I don’t want to pull it out," Trump said of America's role in the alliance. But earlier, he envisioned a less-robust role: "Why is it that other countries that are in the vicinity of the Ukraine are not dealing with — why are we always the one that’s leading, potentially the third world war, okay, with Russia? Why are we always the ones that are doing it?"
This is not dissimilar to his past comments about Syria. "Russia is in Syria," he said last autumn about the fight against the Islamic State. "Maybe we should let them do it? Let them do it."
Despite his later insistence that he would deal with the Islamic State forcefully, there's a theme to Trump's rhetoric that is easy to identify: isolationism. Trump wants the United States to be the world's Trump Tower — a luxurious refuge with a strict screening process where he feels absolutely safe. This is Trump's broader m.o., of course — dropping in on primary states for same-day trips and preferring to battle news anchors from behind the tower's walls.
In a time of fear — fear that President Obama, in an off-the-record conversation earlier this week apparently pegged to cable news programs — Trump's message has been a resonant one.
That his first response to the attacks in Brussels mirrored his broader sensibility should come as no surprise.