Of the three options, a run against John Thune is the least likely choice for Stephanie Herseth Sandlin. Too risky. I think she wants to run for Governor, but is being pressured by Nancy Pelosi and others to stay in the House, at least for the time being.
Would Daugaard beat her for the governorship (assuming it’s an anti-Obama year)?
Now is her chance at Governor (the longest held GOP seat 1979-), if she doesn’t run this time there will be an incumbent Republican in 2014.
Thune leads her comfortably in the polls. I doubt she’ll run for the Senate.