Two American allies, Germany and Japan, already have permission to build the American interceptors, a license that President Trump says he will also grant to Kyiv. In 2022, as fears mounted over Europe’s missile defense capabilities against Russian strikes, the Biden administration granted permission for Germany to build a factory to manufacture state-of-the-art Patriot air defense interceptors. That factory has yet to produce a single Patriot — a sign of the time it can take and how difficult it can be to ramp up production of American weapons abroad, even after winning approval from the United States government to do...