At this point, what realistically could the US do to prevent this? It will continue to spread in other countries, and there's nothing the US can do about that. We can implement more severe travel restrictions, but that has its own issues and it's not recommended by the WHO. That will only be effective for a period of time in the beginning of the virus spread, and they are basically doing that afaik
Im no expert, but besides providing financial or medical aid to to the countries fighting the virus, and helping developing a vaccine/cure, I'm not sure what the US should be doing prevention wise