(CNN) - One's in and one's out.
Oklahoma House Speaker T.W. Shannon officially announced his bid Wednesday for the U.S. Senate seat in his state that's opening up due to Sen. Tom Coburn's early retirement.
Shannon, an African-American who's starting to build a national profile and is considered a rising star in the GOP, made his announcement with statements on Twitter and his website before holding multiple campaign kickoff events.
"It's official: Today I announced my intention to run for the United States Senate," Shannon said in a statement.
"During my time in office, I have been able to help cut taxes by hundreds of millions of dollars, eliminate many millions in waste and duplication, and fundamentally reform our worker's compensation system, saving Oklahoma businesses over one hundred million dollars a year in premium costs," Shannon added.
Minutes before Shannon jumped in, Rep. Jim Bridenstine stayed out. Two lesser known Republicans are also running.
"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."
Coburn announced two weeks ago that he will retire at the end of the current congressional session, ending his second six-year term two years early. The 65-year-old Republican Senator has been battling cancer, but said in a statement that his decision to step down at the end of this year "isn't about my health, my prognosis, or even by hopes and desires."
Last week GOP Rep. James Lankford announced his candidacy. Three other Oklahoma Republicans, six-term Rep. Tom Cole, state Attorney General Scott Pruitt, and former Gov. Frank Keating all have passed on Senate bids.
With Oklahoma considered a firmly red state, the winner of the GOP June primary (and an August runoff if needed) will be considered the favorite to win November's special election, which will coincide with the already scheduled midterm elections. The state's other U.S. Senator, Republican James Inhofe, as well as Mary Fallin, the state's GOP Governor, are both up for re-election in November.
CNN Political Editor Paul Steinhauser and CNN Political Director Mark Preston contributed to this report.