How could it happen? There are certainly political, Constitutional, and (for some) psychological barriers, but, step one could be a two-part response something like this...
- The Federal government will immediately take steps to either relocate or sell all of its assets in California which are located in the counties that choose to leave the United States (see #2). The assets can be purchased by the highest bidder on a piecemeal basis. The proceeds of the sale will be used to finance the new border and to pay off a portion of the existing federal debt.
- Every county in California will be given an opportunity to Leave or Stay. Such a vote, however, must result in two contiguous regions. One will Leave and the other will Stay. Any landlocked, so to speak, counties will belong to whichever nation surrounds them. A period of transition time to move will be provided.
How will California respond to such an offer? I'd love to find out.