Montana Auditor Monica Lindeen (D) won't run for the Senate in 2014, she announced Tuesday.
"After much thought, I've decided against running for the Senate. Montana is my home, it's where my family is and I don't want to leave," Lindeen said on Twitter.
Schweitzer's decision improves the chances for Republicans to pick up the seat of retiring Sen. Max Baucus (D). Rep. Steve Daines (R) is mulling a bid, and would be an early frontrunner if he jumps in the race.
The prospective Democratic field includes state schools superintendent Denise Juneau; Baucus State Director John Lewis; state Supreme Court Justice Brian Morris; EMILY's List President Stephanie Schriock; Lt. Gov. John Walsh; and state Sen. Kendall van Dyk.