Some Senate Democrats think Senate Majority Leader Harry Reid (D-Nev.) should revisit filibuster reform if Republicans continue to block Chuck Hagel, President Obama’s pick for secretary of Defense.

Republicans say Reid promised not to reconsider the nuclear option, a controversial tactic for changing the Senate’s rules with a simple majority vote, after striking a deal with them last month.

But some Democrats say Reid still has the option of changing the rules for the 113th Congress and should consider doing so if Republicans continue to hold up what in past years would have been considered routine business.

"I think it really puts in question the sincerity of the leadership on the other side. Are they serious about moving things forward and do we reexamine these reforms?" said Sen. Mark Begich (D-Alaska).

Begich said Reid could still change the rules with only 51 votes, even though the first session of the 113th Congress is well under way.

"As leader Reid said… that you can still change these rules, you don’t need to on the first day," he added.

Liberal groups and labor unions that pushed Reid to trigger the nuclear option earlier this year were left unsatisfied by the watered-down filibuster reforms he agreed to with Senate Republican Leader Mitch McConnell (Ky.).

Reforming the Senate rules by a simple majority vote is considered so controversial that it is often termed the nuclear option. Reid struck an agreement with McConnell to preserve comity in the upper chamber and help the chances of passing immigration reform and other initiatives.

But some Democrats say Republican efforts to block Hagel call into question that political calculus. The Senate has never used a filibuster to reject a cabinet nominee although it voted down former Sen. John Tower (R-Texas), President H.W. Bush’s nominee to be secretary of defense, in a simple majority vote in 1989.