President Trump’s extreme vetting policy is a temporary, legal and smart use of his national security and immigration powers, the Justice Department said in its legal defense, filed Monday evening, that argues the courts are meddling with the separation of powers. The administration’s lawyers are asking an appeals court to lift a lower judge’s restraining order that has defanged most of Mr. Trump’s Jan. 27 executive order imposing the new vetting policy. The lawyers said immigration law gives Mr. Trump expansive powers to decide whom to let into the U.S. and whom to block, and said that while people who...