The mainstream news media has already figured out that the Trump administration's proposed tariffs on imported copper of 50 percent would dramatically hike copper prices for American industry and raise the price of products containing copper for consumers, which is just about everything electrical. The reason is simple; The United States is a net importer of 45 percent of its copper needs according the U.S. Geological Survey.
All right, you may say, so there will be some short-term pain until the United States develops enough new copper mining and refining capacity to be self-sufficient. First, it's not easy to build such capacity. New mines can take years to build, assuming you already know where the copper is. As for copper refining, few people want such facilities near them so half the challenge is quelling the opposition to any new refining operations. They also take years to build.
Now nobody is going to spend money building new copper mines and refining facilities unless there is a guarantee that the price of copper will stay sufficiently elevated to justify such investments. Even if the proposed tariffs on imported copper were to go into effect, there can be no guarantee that they would be maintained for the couple of decades that investors need for such long-term investments to pay off.