See what comes first there? My allegiance to the Constitution. First, not second. I hope my brothers and sisters-in arms remember that when/if some two-bit CinC decides to circumnavigate the Constitution and try to use them in an attempt to confiscate the guns of the people who have a God given right to defend themselves by whatever means necessary.
I don't know of too many Police Chiefs or county Sheriffs who would be willing to risk the lives of their officers/deputies in a sure-to-fail attempt at door-to-door seizures.
What does that leave? The military.
Brothers and sisters, your first oath is to the Constitution and you have a moral obligation to refuse any order which violates that.