What’s less clear is why this is the moment Trump has decided to take a stand. Though he styled himself a master dealmaker in the business world, he’s been far softer in politics, showing a surprisingly deferential side at the negotiation table, whether his interlocutor is domestic or foreign. He backed down after promising to go after the National Rifle Association on gun control; he shied away from branding China a currency manipulator; he didn’t follow through on threats to investigate the Justice Department or withdraw foreign aid as retaliation for UN votes.

The timing is also peculiar. Trump’s best opportunity to get funding was when Republicans controlled both houses of Congress, during the first two years of his term. But Congress refused, and while Trump griped about it, he never pushed the issue as far as a shutdown. As my colleague Peter Beinart has written, the president shows little interest in actually building the wall. Instead, he appears to view it as an effective political bludgeon against Democrats.