In a surprising announcement, Oklahoma Republican Tom Coburn released a statement Thursday night that he would resign from the Senate at the end of 2014.

Coburn, an ardent fiscal conservative, had been battling a recurrence of prostate cancer but said "this decision isn’t about my health, my prognosis or even my hopes and desires." Instead, he credited his decision to his belief that "public service and politics as a calling rather than a career" and his initial commitment on first running for Senate in 2004 to only serve two terms. Rumors that Coburn would resign were first reported last week by Politico.

The Oklahoma Republican, who had previously served three terms in the House of Representatives from 1994-2000, built a reputation in the Senate as "Dr. No" for his willingness to use obstructionist tactics to block legislation and nominations he opposed. However, Coburn also had a longstanding friendship with Barack Obama, dating back to when they entered the Senate together, and was willing to buck party orthodoxy on a number of issues, including opposition to the War in Iraq.

If Coburn resigns as announced, it would lead to a special election for his Senate seat in deep red Oklahoma. In particular, it would open an opportunity for incumbent Republican congressmen Tom Cole and James Lankford to run for the Senate without endangering their seats. While there are a handful of Democrats in the Sooner State who could mount a competitive race for Coburn's seat, it would still be an uphill battle.

Coburn was one of the two senators not to vote on the omnibus budget bill earlier Thursday.