Donald Trump, apparently feeling emboldened by Attorney General William Barr’s exonerate-y take on the Mueller report and a rowdy rally in Grand Rapids, Michigan on Thursday night, announced on Friday that he may be “closing” the U.S.-Mexico border next week:

The DEMOCRATS have given us the weakest immigration laws anywhere in the World. Mexico has the strongest, & they make more than $100 Billion a year on the U.S. Therefore, CONGRESS MUST CHANGE OUR WEAK IMMIGRATION LAWS NOW, & Mexico must stop illegals from entering the U.S.... — Donald J. Trump (@realDonaldTrump) March 29, 2019

....through their country and our Southern Border. Mexico has for many years made a fortune off of the U.S., far greater than Border Costs. If Mexico doesn’t immediately stop ALL illegal immigration coming into the United States throug our Southern Border, I will be CLOSING..... — Donald J. Trump (@realDonaldTrump) March 29, 2019

....the Border, or large sections of the Border, next week. This would be so easy for Mexico to do, but they just take our money and “talk.” Besides, we lose so much money with them, especially when you add in drug trafficking etc.), that the Border closing would be a good thing! — Donald J. Trump (@realDonaldTrump) March 29, 2019

Given that it is impossible for Mexico to “immediately” end undocumented immigration to the U.S., one could read this threat as more like a promise to close at least “sections of” the border next week, which would seem to be something that would trigger an immediate economic crisis in both countries, given the immediate manufacturing and consumer shortages it would create. Washington Post reporter Josh Dawsey, for what it’s worth, thinks that Trump is referring not to a full closure but to a plan that’s been under consideration for several months which would bar the entry of Central American asylum-seekers on national security grounds. But the White House does not seem to have issued any clarification about whether this is in fact, what the president means by “closing,” and it doesn’t appear that anyone else in the Trump administration, including Homeland Security Secretary Kirstjen Nielsen, had any involvement in Trump’s sudden escalation of the issue.

(Update, 2:30 p.m.: Vox immigration reporter Dara Lind writes, citing a “senior administration official,” that there is actual concern inside the administration that some southern-border ports of entry might have to be closed because of understaffing. She also writes that “everyone else in the Trump administration except Trump” believes that such closures should be an option of last resort. For what it’s worth, staffing-related port closures would seem to be a different beast than the nationality-targeted asylum “closure” Dawsey thought Trump was referring to.)

In any case, Media Matters’ invaluable Fox News/Fox Business tracker Matthew Gertz has likely figured out why this is all happening: Because Trump saw several people demand border closures on last night’s Fox programming. First, on Lou Dobbs’ Fox Business Network show:

Lou Dobbs -- a sometime WH adviser whose show President Trump watches regularly -- and his guests were urging President Trump to follow through and close the border last night. pic.twitter.com/hSEeJOsqTT — Matthew Gertz (@MattGertz) March 29, 2019

(The woman who says immigrants are raping America is named Betsy McCaughey, incidentally.)

Rush Limbaugh, on Hannity, said the same:

From last night's edition of Fox News' Hannity, Rush Limbaugh: "I think the president should shut the border. If he shuts the border and builds the wall, there is nobody, Sean, who can beat him in 2020." pic.twitter.com/73s35ErO32 — Matthew Gertz (@MattGertz) March 29, 2019

(Rush is not correct about suspending immigration between 1921 and 1965. In fact, during that period, there were no restrictions on immigration from Mexico at all; the U.S. even had a work-permit program that permitted hundreds of thousands of migrant workers to cross the southern border legally each year.)

Then there was this guy, a sheriff from Massachusetts who is just laser focused on how the asylum-seeker issue affects the city of New Bedford:

Look, some people might say that this is weird, that the president would suddenly announce an enormously consequential policy, without actually defining that policy or running it by anyone else in the government, simply because Rush Limbaugh and the sheriff of a historic whaling community asked him to. And, frankly, I’d agree. It’s pretty weird.