Donald Trump has been promising to build a border wall ever since the day he announced he was running for president. It was the centerpiece of his campaign—item one on the list of things he would do to Make America Great Again. At his rallies adoring supporters chanted “Build the Wall” in alternation with “Lock Her Up!” The candidate himself could hardly contain his pride when he spoke of the project: his wall would be a thousand miles long and forty feet high! It would have a big, beautiful door and maybe some solar panels! He spoke of it as of a New Wonder of the World, like the Great Wall of China, only greater.

At first Trump promised that the people of Mexico would pay for the wall and be “very happy to do it.” They weren’t, and they didn’t. Later he said that Mexico would pay for it indirectly, with the money the United States saved by renegotiating the North American Free Trade Agreement. Few people knew what Trump meant by this, and even fewer believed him. In any case, the wall failed to materialize. Clearly, if it was going to be built, Congress would have to appropriate the money for it. Given the urgency and enthusiasm with which Trump spoke of the wall during his campaign, one might have expected him to make it a priority once he was elected. But two years went by, with Republicans in control of both houses of Congress, and nothing happened. Some of his supporters grew restive, but Trump assured them he hadn’t forgotten his pledge. He tried to turn last year’s midterm elections into a referendum on the wall—the Caravan was coming!—and got burned: Democrats took back the House of Representatives and made it clear they did not intend to help the president keep his foolish campaign promise. So Trump tried to bully them into giving him $5.7 billion for his wall by shutting down the federal government for more than a month. It didn’t work.

Now, having decided that a second shutdown might hurt his chances of reelection, Trump has at last agreed to a spending deal that includes just $1.375 billion for new border fencing. To distract voters from this humiliating defeat, however, he has also declared a national emergency so that he can build his wall with money Congress budgeted for other projects. This declaration is certainly not Trump’s first abuse of power, but it may be his most shameless. Article I of the U.S. Constitution gives Congress the power of the purse, which means that a president cannot ordinarily spend federal money without congressional approval. Again and again, Trump has failed spectacularly to secure this approval, despite bragging about his skills as a dealmaker.

The fact that it took Trump so long to declare this an emergency strongly suggests that it is not one. So do his own words. Announcing his decision in the White House Rose Garden, Trump said, “I could do the wall over a longer period of time. I didn’t need to do this, but I’d rather do it much faster.” If he didn’t need to do it, then this isn’t an emergency. In real emergencies, such as terrorist attacks or natural disasters, the normal decision-making process ordained by the Constitution, requiring the involvement of Congress, may not be practical: it’s now or never, no time for debate. But there has been plenty of time to debate border enforcement, and there will be plenty of time to continue debating it. The current trickle of illegal border crossings—there are fewer now than there were a decade ago—is not an existential threat to the United States. Trump’s failure to build a wall may indeed be a threat to his political future, but that’s his emergency, not ours.

A coalition of sixteen states has challenged Trump’s plan in the courts. Several other groups have also filed lawsuits, including the ACLU and Texas property owners. A lower court will probably rule against the White House in at least one of these cases, but it will finally be up to the Supreme Court to decide the issue. (It’s safe to assume that Senate Republicans aren’t about to get in the president’s way.) If the judiciary allows Trump to proceed with this stunt, a dangerous precedent will be established, one that should alarm members of both parties. In the future, any president could act in defiance of Congress simply by crying “emergency.” If she were as unscrupulous as Trump, a President Elizabeth Warren could use climate change or income inequality—both problems much more serious than illegal immigration—as a pretext for implementing the Green New Deal by means of an executive order. Of course, Trump himself doesn’t care about precedents; he cares only about saving face. It will be up to others to make sure he doesn’t succeed in sacrificing the Constitution to his vanity.