3) Okay, but only temporarily, right? You said this could “settle” a big part of the immigration debate. But if you don’t like it, the next G.O.P. president can roll it back.

Sure, in theory, but come on: That’s not how anyone on the left is actually looking at this idea — the assumption is that what’s done won’t really be undone, because loss aversion is too powerful, what’s given is hard (for good reasons) to take away, and the politics of stripping millions of people of legal status will be too awful for a Republican Party facing an increasingly Hispanic electorate to contemplate. (Especially if you give President Hillary a term or two in office first.)

But even setting aside the political ambitions here, telling people “sweeping policy change X can happen at the president’s discretion, and if you don’t like you should elect a different president” is pretty much the essence of presidential caesarism. (Which again, to be fair, Posner pretty consistently supports.) I’m arguing that this proposal would amount to a presidential takeover of immigration policy, an executive power grab par excellence; the fact that a future executive could undo doesn’t disprove this argument, it follows naturally from the premise.