Sixteen states have filed a lawsuit in federal court in the Northern District of California against the president's declaration of a national emergency, challenging his use of executive power as unconstitutional.

The complaint seeks to bar the administration from invoking emergency powers to divert money from other federal programs to fund the border wall.

Do states have standing to sue?

The Constitution limits federal judicial power by permitting it only to consider "Cases" and "Controversies." This fundamental requirement of "standing" is about whether plaintiffs—here, the states—have a sufficiently "personal stake in the outcome" of the litigation.

To establish this threshold standing requirement, a plaintiff must demonstrate it has suffered a concrete injury, or that an injury is imminent. That injury must be traceable to the defendant. Finally, a plaintiff must demonstrate that if it wins in court, a court can redress that injury.

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States do not always have standing to sue the federal government. Historically, states did not have the duty or power to enforce their citizens' rights and relations with the federal government, at least according to a 1923 Supreme Court case.

A state does have the right to assert interests in the physical and economic well-being of its populace. This concept of “parens patriae” alone, however, is not enough to give a state standing to sue the federal government on behalf of its citizens.

However, modern courts, including the federal court where this lawsuit was filed, recognize that a state may have its own interests that are independent of the rights of its citizens, and that confer standing on the state to sue the federal government.

California, for example, insists it has standing due to the loss of federal drug interdiction, counter-narcotic, and law enforcement funding caused by the Trump administration's diversion of funding. Colorado, by contrast, asserts that by virtue of being home to many military bases, such as the Air Force Academy, the use of funding for a southern border wall diverts funds for necessary maintenance and repairs to its military bases, and harms Colorado and its economy. When the Trump administration brings its motion to dismiss, the court must consider as a preliminary matter whether these injuries meet the constitutional requirement of standing. In a sense, every decision of every administration has at least an indirect effect on the states. That does not mean that every decision by the federal government is subject to challenge by the states.

Years to declare an emergency?

The states also allege that the president has long claimed a "crisis" at the border wall, but has not declared a national emergency until now. The plaintiffs have plenty of documentary evidence, including speeches and tweets by the president, to support their argument that the president does not honestly consider the border situation to warrant a declaration of a state of emergency.

That might not affect the validity of the declaration itself.

There are some legislative efforts to define a "national emergency." For example, the International Emergency Economic Powers Act (IEEPA) requires "any unusual and extraordinary threat, which has its source in whole or substantial part outside the United States, to the national security, foreign policy, or economy of the United States." The National Emergencies Act, authorizes declarations of national emergencies under Acts of Congress authorizing "any special or extraordinary power."

Federal law contains no real guidance on whether the validity or definition of a national emergency turns on a president's honest belief that it exists. Nor do emergency declarations turn on how long the situation existed prior to the declaration.

When the president declares a national emergency, and states that he "didn't need to do this," it appears to undermine his declaration of an emergency. But a court might just consider these as off-the-cuff remarks that don't undermine the legal effect of the declaration of emergency.

Other presidents have allowed time to pass between the threatening events and the declaration of a national emergency. If a court considers this argument, it might be placed in the awkward position of articulating a set of rules for what presidents cannot say when declaring national emergencies, or a time limit for declaring national emergencies.