FILE: Nov. 13, 2013: Rep. James Lankford, R-Okla., on Capitol Hill, in Washington, D.C.AP

The retirement of Oklahoma Sen. Tom Coburn poses a challenge for Republicans that extends beyond the party trying to preserve his Senate seat.

The conservative lawmaker is considered part of the intellectual core of the GOP whose practical, often bipartisan approach to tackling government waste and other issues will be tough to replace.

“Coburn is one of a kind,” says University of Oklahoma political science professor R. Keith Gaddie. “And anybody who comes along and says he’s the next Tom Coburn — well, he’s not.”

While the two-term senator’s departure at the end of the year will indeed create a void on Capitol Hill and beyond, the race to replace him has quickly turned into a battle over which Republican candidate is the most conservative — and whether Oklahoma really needs another senator like him.

The special election for Coburn’s seat will be held in November. The open race for the seat will be in 2016.

Just days after Coburn’s Jan. 16 announcement, GOP Rep. James Lankford jumped into the race, sparking criticism from national conservative groups.

“Lankford is a quintessential status quo Republican,” Daniel Horowitz, policy director for the Madison Group, wrote after the two-term congressman’s announcement.

Horowitz and his group take issue with several Lankford votes, including the one in favor of the budget bill Congress passed last month.

And he warns that Lankford will likely become the GOP establishment candidate supporting “amnesty” for millions of illegal immigrants living in the United States and be incapable of reversing the “country club culture of Senate Republicans.”

The group has instead put its support behind Oklahoma Rep. Jim Bridenstine, whom it calls “one of the most conservative game-changers in Congress.”

Lankford is waving off the criticism and the less-than-enthusiastic response to his candidacy by the conservative, anti-tax group Club for Growth, which gives Lankford a rating of 78 percent on its voting scorecard.

“I am willing to wage a hard-fought campaign for the opportunity to continue Dr. Coburn’s conservative legacy,” Lankford, chairman of the Republican Policy Committee, said in announcing in bid.

Coburn — a fiscal hawk who served three terms in the House after being elected in the 1994 “Republican Revolution” — was perhaps known for his annual “Wastebook,” which over the years has identified billions in questionable federal spending.

However, his fight against congressional earmarks and his criticism of Pentagon spending over the years has created friction with fellow Senate Republicans and raises questions about whether Oklahoma residents might want their next senator to be more interested in bringing home federal projects, which create jobs and could help improve their economy.

“There’s going to be another Tom Coburn in the Senate,” Gaddie said. “We don’t know who it will be yet. But you just don’t want him in your state.” 

The 65-year-old Coburn, also a medical doctor, was elected to the Senate in 2004 with now-President Obama. They forged a political friendship that includes co-authoring a few bills and has lasted through the president’s second term.

Obama acknowledged his respect for Coburn, who is struggling with reoccurring cancer, by saying after his retirement announcement, “Though we haven’t always agreed politically, we’ve found ways to work together.”

The hometown favorite and long-shot winner in the race might well be T.W. Shannon — who in 2013 became the Oklahoma legislature’s first black House speaker.

Shannon has a law degree and worked for former GOP Rep. J.C. Watts. He is a member of the Chickasaw Nation and was as a chief administrative officer for Chickasaw Nation Enterprises.

“T.W. is for real,” Gaddie said. “And the Chickasaw and Cherokee [nations] have serious money.”