Rep. James Lankford (R-Okla.) announced Monday he will seek the Republican nomination to fill out the remainder of Sen. Tom Coburn's (R) term.
In his announcement, Lankford positioned himself as an heir to Coburn's political legacy, heaping praise on Coburn's crusade against government spending.
“I am willing to wage a hard-fought campaign for the opportunity to continue Dr. Coburn's conservative legacy,” he said.
But Lankford was already receiving pushback from conservatives on day one of his candidacy. Senate Conservatives Fund (SCF) and Madison Project, two national conservative groups known for engaging in primaries to back insurgent candidates, both issued statements panning his candidacy for the seat.
"We won't support Congressman Lankford's bid for the Senate because of his past votes to increase the debt limit, raise taxes, and fund Obamacare," said SCF Executive Director Matt Hoskins in a statement. "We have reviewed his record and it's clear that conservatives cannot count on him to fight for their principles."
In a statement last year endorsing Rep. Jim Bridenstine's (R) reelection, SCF urged Bridenstine to consider running for Senate in the future. Although the group didn't mention him in Monday's statement, he likely remains their pick for the seat.
Madison Project's Daniel Horowitz was more overt in urging Bridenstine to jump in the race as a conservative alternative to Lankford. He called Lankford a "quintessential status quo Republican" and slammed him for his position in support of legal status for immigrants in the US illegally, and said Bridenstine "has too much to offer Oklahoma in the Senate for him to sit this one out."
A source close to Bridenstine told The Hill on Monday that, counter to reports that the congressman might be getting cold feet about the race, he was still very much interested in running and had been getting encouragement from local conservatives. But he could face a challenge for the conservative vote from Oklahoma House Speaker T.W. Shannon, who, a source tells The Hill, is looking very closely at running after receiving numerous calls from supporters over the weekend, urging him to jump in the race.
Still, Lankford enters the race in a strong position, which could become stronger still, if he receives Coburn's endorsement, which a source has told The Hill is expected.
Coburn announced last week he will resign at the end of 2014, despite having two additional years left in his term. He recently suffered a re-emergence of cancer, which he has survived three times already. Coburn said the diagnosis was not the reason he chose to resign.
Lankford, who represents Oklahoma's 5th District, has been in Congress since 2011. Prior to running for office, he was the director Falls Creek Youth Camp, a large Christian youth camp in Oklahoma.
— This report was updated at 2:21 p.m.