Companies once felt an obligation to support American workers, even when it wasn’t the best financial choice,” said Betsey Stevenson, the chief economist at the Labor Department until last September. “That’s disappeared. Profits and efficiency have trumped generosity.” Companies and other economists say that notion is naïve. Though Americans are among the most educated workers in the world, the nation has stopped training enough people in the mid-level skills that factories need, executives say. To thrive, companies argue they need to move work where it can generate enough profits to keep paying for innovation. Doing otherwise risks losing even more American jobs over time, as evidenced by the legions of once-proud domestic manufacturers — including G.M. and others — that have shrunk as nimble competitors have emerged.

One former executive described how the company relied upon a Chinese factory to revamp iPhone manufacturing just weeks before the device was due on shelves. Apple had redesigned the iPhone’s screen at the last minute, forcing an assembly line overhaul. New screens began arriving at the plant near midnight. A foreman immediately roused 8,000 workers inside the company’s dormitories, according to the executive. Each employee was given a biscuit and a cup of tea, guided to a workstation and within half an hour started a 12-hour shift fitting glass screens into beveled frames. Within 96 hours, the plant was producing over 10,000 iPhones a day. “The speed and flexibility is breathtaking,” the executive said. “There’s no American plant that can match that.