Sounds like the SD politicians are having some fun poking the Obama bots...
To your question : State governments, unlike the federal government, are not limited to the US Constitution on federal enumerated powers ?
Also there is the Federal Militia Act of 1792, male citizens were required to equip themselves with firearm and military gear:
http://www.freerepublic.com/focus/f-news/2666765/posts?page=24#24
Thanks for the explano.