That’s the president’s leverage, and leverage, along with his crude take on muscular leadership, is his motivation for doing this. This is the art of the deal with human collateral. And in one sense it’s familiar. Politicians commonly gum up important nominations, tie up precious funds or let bad situations fester to get what they want. There’s a parlance for this. We say that they are holding something or someone hostage.

But the expression is figurative, and the practice tends not to include chain link fences, makeshift blankets and cries in the night. That’s Trump’s new spin on it.

It could be a big political mistake. Sure, his most fervent supporters and the most stubborn tribunes of his fugitive greatness — Tucker Carlson, Laura Ingraham, Ann Coulter — are rallying behind him. Yes, 58 percent of Republicans in a CNN poll said that they supported his current “zero tolerance” treatment of migrant families.

But that disquieting number is nonetheless well below his usual approval ratings from members of his party. And Senate Republicans, showing more independence and defiance than they typically do, signaled on Tuesday afternoon that they wanted to pass legislation to end quickly the separation of families who cross illegally into the country. They’re no doubt worried about the prospects of Republican senators, like Ted Cruz, who are up for re-election in November. Cruz had already denounced what the Trump administration was doing.

What these Republicans perhaps also understand is that how we approach immigration, legal and illegal, is about more than the economy, though that’s an important part of the equation, and more than security, though that’s vital.

In a country of immigrants that has proudly held itself up as an exemplar, it’s about morality. It’s about values. Few aspects of American policy define us in the eyes of the world as sharply as our treatment of immigrants does. Few define us as sharply, period.

We can be tough, yes. But cruel? That’s not in our interests, not if we care to maintain the global sway that we have. Not if we want to hold on to who we are or mean to be: people of generosity and mercy. Not if we’re invested in that “shining city on a hill” that Ronald Reagan so poetically evoked.

He and other presidents, both Republicans and Democrats, saw America as a beacon. They trafficked in inspiration. Trump traffics in fear. That’s where the hostages come in. If they’re young and innocent, so be it. That only ratchets up their utility.