The Wall Street Journal

President Obama ’s decision to legalize millions of undocumented immigrants by his own decree is a sorry day for America’s republic. We say that even though we agree with the cause of immigration reform. But process matters to self-government—sometimes it is the only barrier to tyranny—and Mr. Obama’s policy by executive order is tearing at the fabric of national consent.

The first question to address is Mr. Obama’s legal rationale. At least he finally rolled out a memo from the experts on presidential power in the Justice Department Office of Legal Counsel, but it’s fair to wonder how much time he gave them. The OLC made its justification public about an hour before the speech.

The President’s rationale is “prosecutorial discretion,” but he is stretching that legal concept beyond normal understanding. The executive branch does have discretion about whom to prosecute. But this typically extends to individual cases, or to setting priorities due to limited resources such as prosecuting cocaine but not marijuana use.

Mr. Obama claims he is using his discretion to focus on such high deportation priorities as criminals, but he is going much further and is issuing an order exempting from deportation entire classes of people—as many as five million. Justice’s OLC memo claims there is no such categorical exemption, and that immigration officials can still deport someone if they want to, but the memo offers no measures by which to make that “complex judgment.” In practice it will almost never happen.