When you aren't operating under orders, you are personally liable for everything you do. These militia were not called to muster and are not operating under a proper authority, so they are not more than armed protesters, each individually liable for what they do.
Some have said the photo was a staged event. Some have said how does anyone know if the rifle was loaded or not.
In any firearms safety course that I've been to, you are taught never to point a firearm downrange with people in sight, and to always, always treat every firearm loaded or not, as if it were loaded.
All I can think of saying is that it's a good thing nothing went terribly bad.
Can't we just turn Congress off and then turn it back on again?