The American market is a massive part of some companies yes. But most companies only have a small percentage of revenue in the US.

Listen… the US is just one country. Its a big one and one that buys a lot. But still one country. Many companies can compensate the loss of that market by exploring the many other markets that they have down played. Furthermore, the availability of products that would have gone to the US may even make it cheaper to make and sell products everywhere else than in the US