"After much deliberation, I have decided not to seek the U.S. House or Senate seats in 2014," Juneau states in a Facebook post. "I sincerely appreciate the outpouring of support and encouragement I have received from people all across Montana and the country. It has been very humbling to be considered for such a leadership role representing our great state; however, my decision not to run for Congress is the right one for me at this time."

Juneau joins former Montana Gov. Brian Schweitzer, EMILY's List President Stephanie Schriock and Montana state Auditor Monica Lindeen as potential Democratic candidates who have decided not to run. Schweitzer's decision was a particular blow to Democrats, as the popular former governor was expected to enter the race and likely would have given his party its best chance of holding onto the seat after Sen. Max BaucusMax Sieben BaucusBernie Sanders flexes power on single-payer ObamaCare architect supports single-payer system Trump has yet to travel west as president MORE (D-Mont.) retires.

A top Baucus staffer left his job at the end of last week in order to explore a bid. Other potential candidates include Montana Lt. Gov. John Walsh, state Supreme Court Justice Brian Morris and Montana state Sen. Kendall van Dyk.

On the GOP side, many expect Rep. Steve Daines (R-Mont.) to run.