U.S. President Donald Trump's threat of a 50% tariff on copper imports is raising alarm in the U.S. auto sector, as it could make it even harder for carmakers and suppliers to absorb border taxes and rising costs, executives and industry experts say. The duties on their own may be manageable, but prices of the red metal vital for making cars, in particular in wire harnesses and in motors for electric vehicles, have soared to record highs. The U.S. market is heavily reliant on imported copper, aluminium and steel, and developing new capacity could take years, so users are scrambling to buy metal from a limited number of suppliers, spurring price rises. Added to import tariffs on those metals, as well as higher prices in the United States, the extra costs are compounding the financial strain on carmakers and parts suppliers, interviews with a dozen executives, industry analysts and experts show.