A political unknown just four years ago, Rep. James Lankford has swiftly positioned himself as the front-runner in what could be a crowded GOP primary field to replace retiring Sen. Tom Coburn, R-Okla.

Conservative groups quickly panned Lankford after he announced his Senate bid on Monday. But the 5th District lawmaker starts the contest both with $450,000 in the bank and an established base of faith-based conservatives that GOP operatives argue will be tough for other Senate hopefuls to overcome — especially in a runoff.

“[Lankford] has that incredible base that nobody else has in terms of the Baptist community, which is huge here,” said one Oklahoma Republican operative, who was granted anonymity to speak candidly. “The faith-based community has always been very influential and important in these types of things. I mean, this is the Bible Belt.”

Lankford was the first candidate to jump into the open Senate race after Coburn announced last week he would step down at the end of this Congress. The special election to replace him is scheduled for the same date as the 2014 midterm elections, with a June 24 primary. There will be an Aug. 26 runoff if no candidate gets 50 percent of the vote in the primary.

Three more Republicans — freshman Rep. Jim Bridenstine, state Speaker T.W. Shannon and former Rep. J.C. Watts — are also close to making a decision on the Senate race, Oklahoma Republican operatives said.

Shannon plans to announce an exploratory committee for the Senate race in the coming days, making Watts unlikely to enter the race. Republicans said Watts served as a mentor to Shannon, who worked as a staffer in his congressional office.

Meanwhile, national conservative groups such as the Senate Conservatives Fund and the Madison Project are goading Bridenstine into the race, arguing that Lankford is not conservative enough to replace their standard-bearer, Coburn.

“I’m not opposed to them; I’m not their enemy,” Lankford said in a Wednesday phone interview of the conservative groups seeking alternatives to his candidacy. “We share a lot of the same ideals, but we disagree often on tone.”

While Lankford starts off the race as a front-runner, Republicans caution that a Sooner State primary could prove unpredictable. Just ask Lankford, whose own election to Congress featured the ultimate underdog victory.

In 2010, Lankford directed a popular Christian camp in Oklahoma. Republicans dismissed him as a newcomer in a seven-candidate GOP field to replace then-Rep. Mary Fallin, a Republican running for governor.

But Lankford placed first in that primary, and went on to decisively defeat Club for Growth-backed former state Rep. Kevin Calvey in a runoff.

“It’s funny to me; three years ago I’m citizen Lankford and no one has heard of me and no one gave me a chance,” Lankford said. “Everyone wrote me off, and now suddenly there are groups saying [I’m] the establishment guy.”

The Senate contest is also causing a frenzy downballot.

If Bridenstine enters the Senate race, there will be two open House seats in Oklahoma this cycle. GOP operatives say there is an overwhelming amount of interest from Republican candidates in those seats that will make voters’ money and attention tight in 2014.

Three Republicans already announced bids for Lankford’s now-open 5th District, which includes the center part of the state and Oklahoma City. They include Corporation Commissioner Patrice Douglas, state Sen. Clark Jolley and former state Sen. Steve Russell.

Douglas, who has close ties to Fallin, could have an advantage as the only woman in the race so far. Jolley’s state Senate district lies fully within the bounds of the congressional district, which could give him a built-in geographic base. Russell, a veteran, has an interesting story to tell as he was involved in the capture of Saddam Hussein.

Three other Republicans could announce bids for that seat. They include Oklahoma City Mayor Mick Cornett; state Sen. David Holt, who worked as a staffer to former Speaker Dennis Hastert; and state Rep. Tom Newell, a former professional bull rider.

If Bridenstine enters the Senate contest, at least three Republicans could enter the race. The 1st District includes Tulsa and a part of the northeast corner of the state.

State Sens. Dan Newberry and Rick Brinkley and Tulsa County Commissioner John Smaligo could be Bridenstine successors, according to a recent Roll Call Farm Team column. But sources also noted any number of Republicans could run in an open-seat race.

“We firmly believe in letting free markets and competition sort it out, and the candidate that runs the best campaign is going to finish on top,” said Dave Weston, chairman of the Oklahoma Republican Party.

In all likelihood, none of the vacancies will create pickup opportunities for Democrats in Oklahoma. President Barack Obama lost the state by a 33-point margin in 2012.

Coburn’s Senate seat, Lankford’s 5th District and Bridenstine’s 1st District are all rated Safe Republican contests by Rothenberg Political Report/Roll Call.