Why would Donald Trump find it preferable to shut down the government over congressional refusal to fund his border wall when there was an agreement in place to kick the issue down the road and avoid chaos over Christmas, into the new year, and beyond? Why would he take a position where he has no leverage and where opposition Democrats stand to dictate how the shutdown will end now that Nancy Pelosi holds the Speaker’s gavel?

Credible news reports attribute Trump’s reaction to hearing howls of disapproval from conservative pundits when it appeared he was going to agree to a short-term funding extension without any money for the wall. Ann Coulter called him “gutless” for considering it while Rush Limbaugh characterized the stopgap funding measure as “Trump gets nothing while the Democrats get everything.” Leaders of the House Freedom Caucus said a bill with no money for the wall would cause the base to explode with anger. Reportedly, this was enough to get Trump to change his mind and go all in on the shutdown.

It’s easy to understand how this would affect a president who governs exclusively for the people who show up at his rallies. What may be more important to understand is why his base would be so angry about this particular issue after two years during which the wall hasn’t been funded. Coulter offers an important clue by acknowledging that many Trump supporters saw in his boorishness and petulance exactly the kind of person who would plow ahead with promises to his base despite how unpopular they were to the rest of the country. “Trump’s vulgar narcissism made his vow to build a wall more believable,” she wrote. “Respectable politicians had made similar promises over the years—and they always betrayed the voters.”

This is precisely right. When Trump was running against the Republican establishment, he called them out for lying about their promises to blot out Barack Obama and his legacy, most notably in the form of obliterating Obamacare. In failing to erase the imprint of an administration made possible by an emerging and threatening coalition of non-white, non-male and non-Christian voters, establishment Republicans proved impotent to turn back changes that are at odds with a particular understanding of American greatness. Enter Trump, who understood the grievances of the base better than the establishment Republicans who had exploited them, giving him the opening to exploit them more fully by claiming that only he could fix things because only he really gets it—and because he’s a tough guy who defies convention and gets things done. This has been the basis for the ironclad bond Trump continues to enjoy with his most loyal followers.

Building the wall is by far the most prominent symbol of Trump’s promise to his voters, a tangible manifestation of the idea that Trump can keep out those who in their foreignness threaten, in the minds of Trump’s supporters, to overrun the country. It’s how he can sell them on the idea that chaos reigns on the border when reality says otherwise. The promise of the wall is the essential promise of Trumpism, that only he can reverse the demographic changes that define the 21st Century, the changes that made Obama possible, that threaten white male Christian privilege, and that no one else has been able to stop. Inability to build the wall exposes Trump as a fraud, his promises as empty as those of the Republicans he condemned. Sure, Mexico was going to pay for it, but that can be excused as bravado—as long as the wall gets built.

With Democrats now holding the pursestrings, the last chance to fund the wall has slipped away, making this a perilous moment for Trump by revealing a truth with the potential to tear his coalition apart: The wall is not going to happen. It was never going to happen. Trump can’t build a literal wall and he’s not going to be able to ward off dramatic social change. It was a con when mainstream Republicans promised it ten years ago and it was still a con when Trump out-conned mainstream Republicans in 2016.

Given the stakes, Trump found himself with no choice but to plunge the country into the chaos of a government shutdown. It makes him look like he is standing up for his base, which is why he so proudly took credit for the shutdown in advance. But the act will wear thin if after two years of bluster his supporters are left with only more bluster. That’s why Limbaugh and Coulter chose this moment to demand results. And it comes at a time when Trump can ill-afford to lose his most important cheerleaders as the prospect of accountability for criminal behavior looms in the weeks ahead.