A U.S. Justice Department document that says America can legally order the killing of its citizens if they are believed to be al-Qaida leaders uses the devastating and illegal bombing of Cambodia in the 1960s and ’70s to help make its case. American broadcaster NBC News first reported on the “white paper”—a summary of classified memos by the U.S. Justice Department’s Office of Legal Council—on Monday. The 16-page paper makes a legal case for the U.S. government’s highly controversial use of unmanned drones to kill suspected terrorists, including some U.S. citizens. In making its argument, the document brings up the...