WASHINGTON — The U.S. Justice Department has threatened local and state authorities with prosecution if they fail to cooperate with President Donald Trump’s immigration policies, which include a pledge to deport millions of undocumented immigrants. Citing a constitutional clause concerning division of power, acting deputy attorney general Emil Bove said in a memorandum that “federal law prohibits state and local actors from resisting, obstructing, and otherwise failing to comply with lawful immigration-related commands.” “The Department of Justice shall investigate incidents involving any such misconduct for potential prosecution,” Bove added in the memo issued late Tuesday and published by U.S. media