Would President Barack Obama, by refusing to enforce the immigration laws against millions of undocumented immigrants, be engaging in “domestic Caesarism,” as Ross Douthat charges? The New York Times columnist thinks that “the granting of temporary legal status” violates the Constitution because Congress has itself refused to issue amnesties or offer a path to citizenship.

It’s not entirely clear what Obama plans to do, but if he chooses not to enforce immigration laws against “up to half the country’s population of illegal immigrants,” as Douthat claims, the president wouldn’t be doing anything different from what his predecessors have done (or rather, not done).

Millions of illegal immigrants have lived in the United States for decades, under a semi-official policy that allows them to stay as long as they don’t commit serious crimes—and that, in many cases, allows them to obtain drivers’ licenses. The main effect of Obama's proposal would be to officially recognize current practice. The president cannot suspend or change the law: When he leaves office, the law will remain the same as it was, and the next president will be free to enforce it or not.

The executive branch spends a lot of time not enforcing laws. Congress has illegalized an enormous amount of activity without giving the president the resources to enforce the laws, so the executive has no choice but to make a list of priorities and devote its attention to law violations that, in its opinion, are the most serious. Thus, the IRS doesn’t audit paupers very often. The Justice Department ignores a lot of anticompetitive behavior that might raise prices a bit but not much. The DEA focuses on criminal syndicates rather than ordinary drug users, although both violate federal law. And so on.

Nearly all of this non-enforcement takes place with implicit congressional acquiescence; once in a while, Congress complains because the president’s priorities are not the same as its own. But the president has no obligation to listen to these complaints. The Constitution gave him executive power while preventing Congress from compelling the president to act except by issuing the extreme and usually non-credible threat of impeachment. This is the separation of powers. People like Douthat wrongly think that separation of powers means that the president must do what Congress decides. That’s not the principle of separation of powers; that’s the principle of legislative supremacy, embodied in parliamentary systems like Britain’s, which America's founders rejected.