...you better be pretty damned sure it's an unlawful order.

Like, being ordered to execute civilians, or to execute prisoners.

Being ordered to assist Federal Agents and local law enforcement in preventing the destruction of property, and protecting the lives of Federal Agents and enabling them to do their jobs, at a time when riots like these have, in the recent past, have resulted in deaths and destruction and burning and looting?

And when it's obvious that the local government can't or won't do what's necessary to control the rioters?

Yeah, no one is going to say "That's an unlawful order".