Former Montana state senator Corey Stapleton has announced he will seek the Republican nomination to challenge Sen. Max Baucus (D-Mont.) in 2014, becoming the first well-known GOP candidate to enter the race.

Stapleton finished second in the 2012 GOP governor's primary to former congressman Rick Hill, who went on to lose in the general election to now-Gov. Steve Bullock (D).

Baucus is a top GOP target in a red state. His numbers suffered after he took a leadership role in passing President Obama's health-care bill but have since recovered somewhat.

The GOP primary is expected to be competitive, especially with 2012 Senate nominee and former congressman Denny Rehberg taking a pass on the race.