I don't think you understand, my friend.
Have you ever heard the song "Hotel California" by the Eagles? The final part goes like this ...
Last thing I remember, I was running for the door.
I had to find the passage back to the place I was before.
"Relax," said the night man, "We are programmed to receive.
You can check out any time you like, but you can never leave."
Once we sell it, the buyer isn't really going to "be a part of the U.S. mainland." Sure ... geographically speaking ... the buyer will have a chunk of the North American continent, BUT we won't have a damn thing to do with them after that. We build an impenetrable wall all around California. If anyone from the U.S. wants to go to California, fine ... we let them through the wall ... but, NO ONE comes through going the other way. No flights from California will be allowed to land in the U.S., and any flights heading east from California will either have to cross Canada or Mexico. California will be officially recognized for what it truly is - a leper colony.

The essential American soul is hard, isolate, stoic, and a killer. It has never yet melted. ~ D.H. Lawrence