That’s not how defense works these days. China can barely contemplate invading Taiwan, much less California. Countries are not defended by sprawling physical fortifications along their coasts. They are defended electromagnetically and via missiles and air power that destroy the invading fleet hundreds of miles out at sea. Jesusfuckistan would be too cowardly and too disorganized (states’ rights! Small government!) to invade a Denny’s.
The big concern (if we’re pretending to give this serious analysis) would be ground shipping across the continent. However, without access to the Pacific ports (except possibly Portland, but that is so far up river that it will never have significant deep water capacity), the Democratic US would have Jesusfuckistan by the economic balls. Arrangements would be made.