The Senate Republican leader is raising the possibility of a filibuster of President Barack Obama's nomination of Chuck Hagel to be defense secretary.
Sen. Mitch McConnell told Kentucky TV station CN2 this past weekend that it was "not clear yet" whether Hagel will need a simple majority of 51 votes or 60 votes to secure Senate confirmation.
McConnell declined to say whether he backs the president's pick of the former two-term Republican senator from Nebraska.
He did say opposition is intensifying after Hagel seemed unprepared at his confirmation hearing before the Armed Services Committee last week.
More than a dozen Democrats and two Republicans have announced their support for Hagel, including Nebraska GOP Sen. Mike Johanns this past weekend.
About a dozen Republicans have said they will vote against Hagel.