Sen. Bob Corker (R-Tenn.) has joined a handful of prominent Republican lawmakers willing to break their pledge to oppose all tax increases. 

"I’m not obligated on the pledge,” Corker told CBS's Charlie Rose on Monday morning. "I made Tennesseans aware, I was just elected, the only thing I’m honoring is the oath I take when I serve, when I’m sworn in this January." 

At the same time, Corker has proposed his own fiscal cliff deal that caps deductions but does not raise tax rates. Norquist's pledge bars any net reduction or elimination of deductions and credits without a matching tax cut. 

The no-new-taxes pledge, sponsored by Grover Norquist's Americans for Tax Reform, has been signed by most Republican members of Congress. But many signed decades ago; some listed members announced during last year's debt negotiations that they no longer support the pledge. With difficult fiscal cliff negotiations in the works, the group of Republicans who question the pledge's usefulness is growing.  

Sens. Saxby Chambliss (Ga.), and Rep. Peter King (N.Y.) both declared recently that the pledge may be out of date. Sen. Lindsey Graham (S.C.) said he was willing to set the pledge aside if Democrats agree to entitlement reform.

But Norquist says he isn't worried about a mass defection. 

“I don’t think between now and 2014 that either the South Carolina senator or the Georgia senator will vote for a tax increase,” he predicted in an interview with The Fix.

While no threats of primary challenges have yet emerged, lawmakers will likely be thinking of two troubling examples: the handful of members who lost their seats over the 2008 Troubled Asset Relief Program (TARP) bailout and George H.W. Bush's loss after breaking his pledge to not raise taxes.