The US is too big to make crossing it by train (even high speed) plausible when airplanes are a thing. High speed trains proved successful in medium distances. It sounds reasonable for California (LA-SF) and for east coast cities (New York-Washington), but covering the entire US is really not very useful.
However, I'm pretty sure that a large part of the costs of the California rail are related to private land, which probably isn't an issue through the majority of the route.