One Wonders Who These Marines Are Defending

Patently obvious, I'd say. In recent years we've seen the blurring of distinction between police and the military and the dismantling of Habeus Corpus, and I can assure you that it ain't because the Russkies are about to invade. This is just another in a long line of exercises violating Posse Comitatus to desensitize the military, police and citizens to accept what just a short time ago was considered completely unacceptable.
In case it isn't obvious, "Civil disobedience will not be tolerated".

Marines bringing combat training to Indy

"U.S. Marine helicopters will land at the old Eastgate Consumer Mall, Brookside Park and other Indianapolis locations when the city becomes a mock battlefield next week.
About 2,300 Marines from the 26th Marine Expeditionary Unit, based at Camp Lejeune, N.C., will conduct urban warfare training from Wednesday through June 19 in and around Indianapolis. (...)
The Marines will practice firing weapons, conducting patrols, running vehicle checkpoints, reacting to ambushes and employing nonlethal weapons, according to a statement."