Story highlights Roy Moore has put GOP leaders in an increasingly difficult position

He's running as the Republican nominee for a Alabama special election

(CNN) House Speaker Paul Ryan called allegations leveled against Alabama Republican Senate candidate Roy Moore about pursuing relationships with teenage girls and committing sexual assault "credible" and that he should step aside.

"He should step aside," Ryan told CNN Tuesday morning. "Number one, these allegations are credible. Number two, if he cares about the values that he claims to care about, then he should step aside."

Ryan becomes the latest high-profile Republican voice to call on Moore to step aside, following more than two dozen Republican senators, including some of whom have suggested voting to expel Moore from the Senate should he win the December 12 special election.

The flood of condemnation and calls to step down replaced what had been days of heavily caveated statements defined by senators calling for Moore to step aside "if" the allegations "were true." Starting Monday with Ryan's counterpart, Senate Majority Leader Mitch McConnell, the tone from national Republicans shifted dramatically.

An Alabama woman alleged Monday that Moore sexually assaulted her when she was a teenager. Moore called the accusation "absolutely false" in a statement in Gallant, Alabama, later Monday, denying that he knew the woman.

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