IN the months since President Obama first seem poised — as he now seems poised again — to issue a sweeping executive amnesty for millions of illegal immigrants, we’ve learned two important things about how this administration approaches its constitutional obligations. First, we now have a clear sense of the legal arguments that will be used to justify the kind of move Obama himself previously described as a betrayal of our political order. They are, as expected, lawyerly in the worst sense, persuasive only if abstracted from any sense of precedent or proportion or political normality. Second, we now have...