If you're single with no children, you live up to your commitment to the Army. If you ever receive orders to engage in activities against American citizens that go against the Constitution, you refuse to obey those orders. For example, National Guard members were ordered to confiscate firearms from law-abiding citizens in New Orleans during the Katrina disaster. That would be an example of what NOT to do.
If you have a family, things can get messy. You'll have to weigh the situation. But if you do have a family, devise a plan of what to do and possibly where to go for different scenarios. Teach them how to look out for and look after themselves.