I keep hearing that states can't secede. But let's say one does.

[hlthe2b]

20. Their economy folds day one, no functioning airports, shipping ends from nearly every US company

due to the uncertainty of travel into the newly developed border, their residents lose all government aid including SS and Medicare, and no security of their current banking (no FDIC)... So, whether or not it incites a military response, it would be like a mini Brexit only with the impacts IMMEDIATE and magnified by infinity. States like Texas and Florida would think they could survive that, given their substantial coastlines allowing trade outside the US, but that would make (at least Florida) at risk from outside players in a time of uncertainty, and without the US military, who would protect them from a modern-day Cuba Missile Crisis or targeted attacks from unstable forces in those countries that we've been facing the flood of refugees emerging from (like Venezuela)?