President Trump ordered General Motors Co. to sharply ramp up the production of ventilators to treat coronavirus patients, turning to a wartime presidential power that he had been reluctant to use. Mr. Trump on Friday invoked the Defense Production Act, or DPA, which dates back to the Korean War and gives the president powers to require businesses to produce goods tied to national defense. For weeks he had said that the threat of invoking the DPA was sufficient. Previously he likened using the DPA to nationalizing…