I don't know what the actual protocol is, and have read that state-to-state pacts exist.
Clearly, "calling out the Guard" is not a one-size-fits-all proposition. The NG may be called to search people entering the SuperDome, or it may be called to quell insurrection. Blaco did call for something on Thursday, but I don't know exactly what that was.
"The task before us is enormous, but so is the heart of America."