This argument’s logic, at once consistent and deliberately obtuse, raises one obvious question: Why stop at half? (Activists are already asking.) After all, under this theory of what counts as faithfully executing the law, all that matters is that somebody, somewhere, is being deported; anyone and everyone else can be allowed to work and stay. So the president could “temporarily” legalize 99.9 percent of illegal immigrants and direct the Border Patrol to hand out work visas to every subsequent border crosser, so long as a few thousand aliens were deported for felonies every year.

The reality is there is no agreed-upon limit to the scope of prosecutorial discretion in immigration law because no president has attempted anything remotely like what Obama is contemplating. In past cases, presidents used the powers he’s invoking to grant work permits to modest, clearly defined populations facing some obvious impediment (war, persecution, natural disaster) to returning home. None of those moves even approached this plan’s scale, none attempted to transform a major public policy debate, and none were deployed as blackmail against a Congress unwilling to work the president’s will.

And none of them had major applications outside immigration law. No defender of Obama’s proposed move has successfully explained why it wouldn’t be a model for a future president interested in unilateral rewrites of other areas of public policy (the tax code, for instance) where sweeping applications of “discretion” could achieve partisan victories by fiat. No liberal has persuasively explained how, after spending the last Republican administration complaining about presidential “signing statements,” it makes sense for the left to begin applying Cheneyite theories of executive power on domestic policy debates.

Especially debates in which the executive branch is effectively acting in direct defiance of the electoral process. This is where the administration has entered extraordinarily brazen territory, since part of its original case for taking these steps was that they supposedly serve the public will, which only yahoos and congressional Republicans oppose.

This argument was specious before; now it looks ridiculous. The election just past was not, of course, a formal referendum on the president’s proposed amnesty, but it was conducted with the promise of unilateral action in the background, and with immigration as one of the more hotly debated issues. The result was a devastating defeat for Obama and his party, and most polling on unilateral action is pretty terrible for the president.