Instead, Noem said, she'll run for reelection to the House. Noem pledged to work to help a Republican win back the seat to be vacated by retiring Sen. Tim JohnsonTim JohnsonFormer GOP senator endorses Clinton after Orlando shooting Housing groups argue Freddie Mac's loss should spur finance reform On Wall Street, Dem shake-up puts party at crossroads MORE (D-S.D.).
In late May, Noem told The Hill that she was discussing a potential Senate run with groups interested in her candidacy, though she wouldn't elaborate.
She was considered a more conservative alternative to the only announced Republican in the race, former Gov. Mike Rounds.
But some Republicans were worried that if Noem launched a primary challenge against Rounds, that would ultimately weaken the eventual nominee and jeopardize Republican chances at the seat.
Noem's decision not to run eliminates a hurdle to Rounds's nomination, but outside conservative groups are still actively looking for a potential challenger.