No corporation is building a factory based on a policy that has a lifetime of four years.
Your second sentence indicates the more significant problem though, because that uncertainty on timelines makes even the 3-4 year time horizon questionable. Nobody is going to invest anything based on tariffs that may go away or change next week and the only way you can tell if they're sticking around is waiting so long you don't have time to make the investment any more.
It might be different if Trump came in with a clear, transparent tariff plan on day one. But they're already all over the place and being implemented in extremely unpredictable ways. Some people might argue his unpredictability is an asset in general, but it's absolutely not in this case.