Oklahoma House Speaker T.W. Shannon is forming an exploratory committee to look more closely at a potential run in the special election for retiring Sen. Tom CoburnThomas (Tom) Allen CoburnThe real disease: Price transparency key to saving Medicare and lowering the debt Mr. President, let markets help save Medicare Pension insolvency crisis only grows as Congress sits on its hands MORE’s (R-Okla.) seat, multiple sources tell The Hill.

Shannon’s office declined to comment, but sources say he's now expected to run.

One source tells The Hill Shannon has received dozens of calls from supporters “very enthusiastically encouraging him to run” since Coburn’s announcement last week that he’ll retire at the end of the year.

Shannon would run as a conservative alternative to Rep. James Lankford (R-Okla.), who entered the race Monday to considerable pushback from conservative groups.

"We have reviewed his record and it's clear that conservatives cannot count on him to fight for their principles,” Senate Conservatives Fund Executive Director Matt Hoskins said in a statement after Lankford announced.

That group endorsed Rep. Jim Bridenstine (R-Okla.) for reelection and urged him to run for Senate last year. Bridenstine would likely get the support of most of those deep-pocketed national conservative groups if he ran.

But with Shannon in the race, Bridenstine wouldn’t be guaranteed to pick up the anti-Lankford mantle, and the two run the risk of splitting the conservative vote and giving Lankford an opening to take the primary.

More likely, observers say, is for the primary to head to a runoff, where Lankford and an alternative candidate would face off.

Shannon’s supporters believe he could have a shot at making it to the runoff because he’s got the strong political ties within Oklahoma that Bridenstine lacks, and the state House speaker has also been a stronger fundraiser than the congressman. Shannon has raised his profile within the state over the past year, as he was named one of the Republican National Committee’s “Rising Stars.”

Sources close to Bridenstine say he hasn’t yet made his decision, and it ultimately wouldn’t be based on what any other candidate does.