Donald Trump’s brief moment of presidential behavior appears to be over.

On Aug. 21, President Donald Trump delivered a measured, respectable prime-time address explaining his new policy on the complex problem of Afghanistan. It was one of the most serious and sober-minded speeches of his seven-month-old presidency.

A day later, Trump removed his rhetorical cuff links and returned to the political street brawling he seemed to love as a candidate. Trump held a rally in Phoenix — where local officials urged him not to come — rousing several thousand supporters with familiar rants: the media is out to get him, the NAFTA trade deal is terrible, Democrats are obstructing his agenda.

While airing these grievances, Trump said he’d shut down the government if Congress doesn’t appropriate $1.6 billion for the wall he wants to build along the U.S. border with Mexico. Government shutdowns aren’t the worst thing in the world, since essential functions continue: Social Security checks keep going out and the Pentagon remains on alert. But voters hate shutdowns. The last time this happened, in 2013, a buoyant stock market flat-lined and the economy lost $24 billion in output before Congress funded the government after a 16-day impasse. Congress’ approval rating plummeted to 8.5%, the lowest level on record.

Government shutdown threat is a bad idea

Would Trump really go to the mat for a mere $1.6 billion, which is .04% of all federal spending? Nobody knows, maybe not even Trump. But threatening to shut down the government is a foolish move that could harm Trump more than anybody else.

Trump probably hopes his threat will persuade Republicans who control Congress to throw in the towel and just give him the $1.6 billion. They might. But they might not, for a few important reasons. First, Trump’s relationship with Congressional leaders is severely frayed, with the New York Times reporting that Trump and Senate Majority Leader Mitch McConnell aren’t even on speaking terms. Trump’s blunt criticism of McConnell and other should-be allies in Congress is part of the reason. Trump has also shown little interest in the usual horse-trading that gets bills passed. It’s his way or the highway, which so far has led to the highway. (See: Better Care Reconciliation Act, b. 2017, d. 2017.)

One other problem: Virtually all Democrats and some Republicans think Trump’s border wall is a bad idea, most likely leaving the Senate short of the votes needed to pass border-wall funding as a standalone measure. At least four Republican senators from states along the border—John McCain and Jeff Flake of Arizona, and Ted Cruz and John Cornyn of Texas—have problems with Trump’s wall. They might cave amid larger concerns over shutting down the government. Or McConnell might be able to buy their support by padding a budget bill with other goodies that benefit their states. But it’s worth noting that Trump has now bashed McConnell, McCain and Flake by name, in addition to lampooning Cruz as “lyin’ Ted” during the campaign. These are not pals who will have Trump’s back when the chips are down.