Always a good topic. I have cousins in Texas who think, incorrectly, that Texas is the only state in the Union which can "legally" secede. I keep reminding them that Texas has tried this a few times already and it's never going to happen.
Ultimately, there would need to be something catastrophic underlying a secession.
Check this article out from WAPO:https://www.washingt...m=.475cb8a9ec8b
I always find a reason to drop her name, but Octavia Butler wrote a novel where Alaska seceded from the Union and joined Canada, then went to war with the US and won! The backdrop there was economic and environmental collapse, and Alaska's distance helped too. Referring to the article, Alaska took Option 3 and 4, by declaring itself a part of Canada, and then defeating the US army. But even that was a bit far fetched once you drill down into what's really going on with the Constitution.
The Constitution doesn't acknowledge separate states ... period. Ever. Never has and never will. There is no process of leaving the union and it's about as tangible as saying London can secede from Great Britain. (Or look at East and West German - it was one country split, but one country nevertheless). The US may have started out as independent colonies (with different money and time zones) but two-hundred years later (and a brutal Civil War where the South didn't stand a chance) the US is one country.
Of course ... history is written by the victor. If the South had the industrial complex necessary to beat the Union things might have been different.
Also, and I know I'm rambling, but this topic is very interesting and comes up often, we would have to consider loyalists within the army and militias. Like the South, any seceding state would be stealing from the US government, and if the US would allow it peacefully they may want their property back. So all military hardware, clothing, etc. would have to be sent back. The new country would need aid from somewhere, (hence Butler aligning Canada with Alaska) and wouldn't win a conflict on it's own (see the South).
I could go on for days ... which usually happens when my cousins visit.