Thune shot to national prominence in 2004, when he defeated Senate Democratic Leader Tom Daschle, in a narrow and hard-fought race in a red state. He was just re-elected unopposed in 2010.
Pawlenty served two terms as governor in Dem-leaning Minnesota. He did not seek re-election this past November, and was narrowly succeeded by Democrat Mark Dayton. He is now set to embark on a book tour, apparently in order to test his national appeal.