I’ve read several times that secession will occur through a more gradual process and to some degree has already started. The examples given are states making new laws that ignore federal laws. Legalization of marijuana by several states is sited. But states are drafting other laws as well specifically stating federal law will not be enforced.
The theory is that this will continue until the separation is so large that states will pull away and the fed won’t have the ability to prevent secession.