On Wednesday, we get second-quarter earnings from Alcoa, the major aluminum manufacturer. And that may offer clues about how the escalating trade battle is playing out for domestic manufacturers and workers now that tariffs on aluminum and steel are a reality. The United States is now charging 10 percent tariffs on imported aluminum from Canada, the European Union and other countries. This puts Alcoa’s U.S.-made aluminum at a competitive advantage in the domestic market. But it may not help reopen aluminum plants that were already shuttered, thanks in part to low-cost foreign competition. And Alcoa depends on supply chains that are part of a global market in an environment with escalating trade tensions.