Protectionism. Musk stands to gain a ton if there's less competition from imported EVs, and that's true for a lot of other products that American companies make. If you can just throw a few million at a presidential campaign and essentially guarantee your competitors will have a 10-60% disadvantage, those few millions can turn into billions in profit.

On paper, the goal seems to be to spur companies to return to the US, but I think the net impact will be higher prices for Americans and reduced trade w/ other countries due to retaliatory tariffs.