The Ninth U.S. Circuit Court of Appeals violated both judicial precedent and the Constitution’s separation of powers in its ruling against President Trump’s executive order on immigration. If the ruling stands, it will pose a danger to national security.

Under normal rules of standing, the states of Washington and Minnesota should never have been allowed to bring this suit. All litigants, including states, must meet fundamental standing requirements: an injury to a legally protected interest, caused by the challenged action,...