That's not really what NATO is for and it'd depend a lot on what the actual events looked like. If it's frameable as armed violent uprising/terrorism being controlled then it's much less likely to pull explicit foreign intervention and the prototypical '2A to protect against a tyrannical government usage' will almost definitely fit that bill.
Correct, it depends on the size of the uprising. Further this is still an illegal order to kill US citizens. And with that once the order comes down chaos will ensue in the ranks.
