Our immigration system is broken and Congress has shamelessly refused to fix it. Of course, this unfortunate circumstance doesn’t give the executive branch the power to institute reforms itself. Yet through a recently announced policy known as Deferred Action for Parental Accountability (DAPA), President Obama has given partial legal status to more than four million illegal migrants, entitling them to work authorizations and other benefits. This unilateral action is good policy, bad law, and terrible precedent. Perhaps most importantly, it violates the separation of powers and is thus unconstitutional. In what is becoming a routine occurrence under this administration, 25 states have sued the federal government in response to this executive action. The case is now before a federal district judge in Brownsville, Texas, who is entertaining the plaintiffs’ motion to enjoin DAPA. The Cato Institute, joined by law professors Josh Blackman, Jeremy Rabkin, and Peter Margulies, has filed an amicus brief supporting the motion. It's highly unusual for Cato to file at the district court level—indeed amicus briefs of any kind are unusual in this forum—but this is a highly unusual situation. To be clear, we support comprehensive reform that would provide relief to the aliens protected by DAPA (among many other goals), but it’s not for the president to make such legislative changes alone. President Obama has defended his action by citing past deferrals for (1) battered and abused aliens, (2) aliens involved in human trafficking, (3) foreign students affected by Hurricane Katrina, and (4) widows of U.S. citizens. But these deferred actions, to the extent they're relevant here, served as temporary bridges from one legal status to another, not tunnels that undermine legislative structure or detours around the law to hitherto unknown destinations. Moreover, they were several orders of magnitude smaller than DAPA, in the tens of thousands not the millions. Most significantly, they were all approved by Congress. None of these principles holds true for DAPA. The administration itself stated the applicable test in the memorandum setting out DAPA’s legal justification: “an agency’s enforcement decisions should be consonant with, rather than contrary to, the congressional policy underlying the statutes the agency is charged with administering.” This executive action represents a fundamental rewrite of the immigration laws that is inconsistent with the congressional policy currently embodied in the Immigration and Naturalization Act (INA)—a policy that, again, those who joined this brief by no means endorse. As Prof. Blackman explains in a new law review article, DAPA is in palpable tension with the INA, implementing under the guise of executive discretion wholesale waiver/suspension/deferral that swallows the enforcement rule. Indeed, Congress rejected or failed to pass immigration-reform bills reflecting this policy several times, so executive power in this area is "at its lowest ebb," to use Justice Robert Jackson's famous formulation from the 1952 Steel Seizure Case. In our constitutional architecture, executive action based solely on Congress's resistance to presidential policy preferences has no place. While we agree that the immigration laws need to be overhauled and sympathize with the plight facing undocumented aliens, the path designed by the Framers for implementing needed reforms goes through the halls of Congress. Unilateral exercises of power such as DAPA undermine the separation of powers and ultimately the rule of law.