As work absences by air traffic controllers started causing flight delays, as IRS understaffing began to threaten tax filing season, as 800,000 federal government workers missed another paycheck — and as Republican senators began to unload on Majority Leader Mitch McConnell and Vice President Mike Pence about the growing fallout from the government shutdown and the utter lack of any viable strategy by the White House to end it — President Donald Trump did the right thing Friday by agreeing to a temporary plan to reopen the government. But let’s not call this crisis over just yet. The next three weeks provide ample opportunities for President Trump to plunge us back into chaos again, and his vow to shut down the government again or use an executive order to build a border wall without congressional approval show he’s fully prepared to do it.

It should by now be clear that Democrats in Congress will not support funding for the border wall and that voters do not support shutting down the government to try to force their hand. We doubt the public will be any more receptive to a president abusing his authority to get his way, and even some conservatives are warning Mr. Trump against declaring the situation at the border an emergency for fear that a future Democratic president will follow that precedent — perhaps to deal with an actual emergency, like climate change.

In a sane world, President Trump would spend the next three weeks negotiating with Democrats to get substantial funding for other border security efforts — more support for the border patrol, enhanced technology and other measures — even physical barriers in some places — that are likely to be more effective than the “big, beautiful” wall Mr. Trump has been demanding. House Democrats have reportedly been working on a package of border security spending equivalent to or greater than the $5.7 billion Mr. Trump wanted for his wall. He should take it and declare victory.

For a time, during his speech announcing the deal, it sounded like that was just what President Trump intended to do. He spoke of consulting with experts on the most effective strategies for increasing security on the border and at ports of entry and working with Democrats and Republican in Congress to fund and implement them. But then he veered off again into MAGA rally-style fearmongering about the supposed crisis at the border with a list of dubious if not outright false claims about the level of crimes committed by immigrants and the effectiveness of a wall in stopping them. By the end of the speech, he was back to insisting that we need to “build a powerful wall or steel barrier” and vowing to shut down government again or use his executive authority to do it if Democrats don’t agree by Feb. 15.

We would like to believe that was all just bluster to satisfy his political base and give him the room to strike a reasonable deal. But considering how mercurial he has been and how lavish he has been to the most strident border alarmists, we’re not betting on it. He walked away from a bipartisan deal to keep the government open in December, and when the immediate pain of the shutdown recedes, he’s fully capable of doing it again in February. The more people declare his decision to reopen government a capitulation by the president and a win for Democrats — which it is, since this turn of events is more or less exactly what House Speaker Nancy Pelosi has been demanding — the more likely he is to lash out. And when he does, 800,000 federal workers will bear the brunt once again.