What would the blue states do - threaten to declare war on us if we didn't stay put? 600,000 Americans died the last time the feds tried to stop a secessionist movement. Americans don't have the stomach for such bloodshed and carnage today. Especially not on their own soil.
Besides, they don't have the manpower (or firepower) to stop the red states from going their own way, if that's what they're determined to do.
No, it would be a political (and economic) re-alignment. Nothing more.
threaten to declare war on us if we didn’t stay put?
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Yes. US troops and Mexican troops. You underestimate the demand for power and submission.