It is their duty under the insurrection Act when all three branches of govt fail in their constitutional duties to protect the people, as was done by our judicial, legislative and executive branches earlier this year.
Just because it's their duty doesn't mean they will fulfill it, same could be said for any of the traitors from the "commander in chief" to the "supreme" court to congress. The upper levels of the military are compromised just like the rest of the swamp, to what degree I'm not entirely sure but I sure don't have a lot of confidence in the upper ranks. It boils down to people, as the founders said the system will work with a moral people and isn't designed to work without that qualifier. We've had top generals virtue signaling and going woke, we've had open communists make it most of the way through west point, we've had judges openly laughing about legislating from the bench and referencing foreign court actions as if they had bearing in our Country, we've had presidents mock the Constitution. Ask anyone whose spent significant time in the military the officers are mostly careerists and back stabbing politicians and doubly so at the highest ranks. Supposed "mad dog" mattis has even shown his true colors lately. It's down to us as individuals to hold what ground we have left and start nibbling back. At best it will take generations, at worst it won't happen.
