Unless the regular army takes the side of the unorganized militia we would be little more than a short field exercise and mop up operation.
Also consider that the militia would have to communicate much as Al Kada does by courier. The intelligence services electronic surveillance technology would be able to zero in on members that so much as made a telephone call to one another. Texting, Email and landlines would all be monitored. I also suspect that all of the existing organized militia members are already known and would be picked up within hours of Obama making such a move.
There's ways to deal with that: 1) cyphers, especially useful would be a book-cypher as (123,18) would be unintelligible w/o the look-up table; 2) non-electronic methods of communication (paper, mouth, etc); 3) generating so much garbage traffic that data-mining becomes useless.
Furthermore, you would have to control/subdue 300+ million people -- Afghanistan proves just how impossible it is to dominate a people who refuse to be so dominated.