Entered:
https://uselectionatlas.org/POLLS/PRESIDENT/2012/polls.php?action=indpoll&id=4620120723171
Of the four SD polls we have, three are from Nielson Bros.
Back in December they had an R + 20 result, but in February it was down to R + 9. The only other poll in the database is a PPP poll from January 2011 that was R+6. South Dakota is typically only a fraction more Democratic than North Dakota, but the polling has been more divergent, but whether Nielson Bros. or DFM Research (which has two of the three ND polls in the database) is at fault, I can't say.
I think DFM is a little too favorable to Romney and a little too favorable to Heitkamp. They're probably trying to show that Heitkamp is competitive despite Romney crushing Obama by 19. Anyway, I think Obama is probably down 12 to 15 in North Dakota, 15-18 once the undecideds come in, but not right now.