Rep. Jim Bridenstine, R-Okla., announced Wednesday that he will not run for the open Senate seat being vacated by retiring Sen. Tom Coburn, R-Okla, in 2014.  

Outside groups such as the Senate Conservatives Fund and the Madison Project put pressure on Bridenstine to enter the contest as a conservative alternative to GOP Rep. James Lankford, who already announced his candidacy.  

“Since Dr. Tom Coburn’s retirement announcement, I have been honored and overwhelmed by encouragement to succeed him as Oklahoma’s senator,” Bridenstine said in a statement. “After giving this matter serious consideration and prayer, my family and I have decided I will not to run in the special election to complete Dr. Coburn’s term.”  

As Bridenstine announced he won’t run, state House Speaker T.W. Shannon announced he will enter the race, setting up a two-candidate GOP primary between Shannon and Lankford.  

A two-candidate field all but eliminates the possibility of a run-off – which is triggered if no candidate receives a majority of the vote.  

That shortens the time frame of the election – which will likely be decided in the GOP primary in this strong conservative state. President Barack Obama lost in Oklahoma by a 33-point margin in 2012.  

The primary is scheduled for June 26 .  

While outside groups made clear they don’t support Lankford’s candidacy, it’s unclear whether they will support Shannon in the race.  

Oklahoma Republican operatives, as well as GOP Rep. Tom Cole, say outside-group spending in the Sooner State has fallen flat in recent cycles . Yet a shorter time frame for the race would make outside group money go further for television advertising, giving the groups more sway.  

The Oklahoma Senate race is rated a Safe Republican contest by Rothenberg Political Report/Roll Call.