You are seriously exaggerating the “decades” components of this. The U.S., since it already is a large and wealthy economy, always has capacity in memory (Micron), foundry (Intel, GlobalFoundries), and shipbuilding (Northrop, etc). The issue with the U.S. would be that it would need to scale should an exogenous foreign shock happen. But an exogenous foreign shock would simultaneously increase the profitability of entering the sector, from both a firm and individual perspective so it would at most take a few years. See for example, how quickly supply chains unsnarled themselves and how inflation in the U.S. is back to normal after 16 months despite some very large supply shocks - Covid, Ukraine; interest rate hikes ; and large demand shocks - very large fiscal deficits.
what’s more: Japanese and South Korean firms export to the United States in order to make money themselves; without final American demand, those firms lack the scale to compete effectively