Re: Starfleet Marine Corps
Local troops could get federalized and deployed in support of Starfleet but I don't think there'd be much need for that.
Actually, there was supposed to be a scene in Homefront / Paradise Lost where that exact thing happens: we would have seen Jaresh-Inyo "federalizing" United Earth forces to assist in the crisis. But it got cut for time.
"A hot dog at the ballpark is better than a steak at the Ritz." - Humphrey Bogart