If the federal government has to prioritize its resources, why should we care if the president decides to make enforcement decisions for broad categories of people? A big reason is deterrence. Zachary Price, a visiting assistant professor at the University of California Hastings College of the Law, lays out this argument nicely in a recent piece for the Vanderbilt Law Review. Even if the federal government lacks resources to enforce a law on everybody, he points out, mere threat of enforcement can get people to comply. But once you’ve waived away enforcement for a group of people, they won’t bother to obey. Eliminating the deterrent, Price argues, undermines the law—and thus crosses the line from prosecutorial discretion to “law making.”

That’s a pretty powerful argument for why something like DACA exceeds the boundaries of presidential authority—and what separates it from the Morton Memo. Under DACA, thousands of undocumented immigrants have been granted deferred status and no longer fear deportation, at least temporarily. The Morton Memo, on the other hand, never removed the threat of deportation, because officers could still make judgments on a case-by-case basis. That’s why, under Price’s argument, the Morton Memo is a legal use of prosecutorial discretion and DACA is not.

But that’s not the end of the story. This analysis elides over a key point: Congress does not create laws just to discourage certain actions. It also has many other priorities in mind. The president can implement legislation in a way that downplays the importance of deterrence while promoting other values in a way that stays faithful to the statute.