The Constitution — yes, that again — says that presidents "shall take care that the laws be faithfully executed." The Framers, who were parsimonious with words, perhaps included the adverb for the reason Noah Feldman of Harvard Law School suggests: "The Constitution recognizes that the president can't necessarily enforce every law. But it requires a good faith effort." So, the intent of any nonenforcement matters: Is it to husband scarce enforcement resources? Or is it to vitiate a law?