The devil is in the details.
We can also declare a city or state a Sanctuary for anything Democrats want to take away. There are already numerous Sanctuary States for the Second Amendment. Do the same to defend freedom of speech or other Constitutional rights.
You don’t have to secede. You can maintain the rest of the legal system. And you can add or remove legal protections as necessary.
Furthermore, you can do things on a county or city level ... so you don’t have to kick out all the blue city voters, just ignore them.