> then that access may not be reliable in the event of conflict with China.

Some might call that poor pre-planning. If you're about to go to war with your biggest supplier, you'd be well advised to stock up on supplies before firing the first shot.

Reducing the diversity of your supply chain and instead making your self so incredibly vulnerable that all an adversary has to do is fubar your own domestic supply chain (because imports have long been banned) is way less robust than maintaining imports. If you actually wanted what you claim, you'd allow imports while taxing or subsidizing until they look roughly break even with domestic offerings.