Grover Norquist’s anti-tax pledge has been a sacred and unchallenged keystone of the Republican platform for more than two decades, playing a central role in almost every budget battle in Congress since 1986. But Norquist and his pledge, signed by 95 percent of congressional Republicans, are now in danger of becoming Washington relics as more and more defectors inch toward accepting tax increases to avert the “fiscal cliff.”

On Monday, Sen. Bob Corker (Tenn.) became the latest in a handful of prominent Republican lawmakers to take to the airwaves in recent days and say they are willing to break their pledge to oppose all tax increases.

“I’m not obligated on the pledge,” Corker told CBS’s Charlie Rose. “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.”

House Majority Leader Eric Cantor (R-Va.) also suggested Monday that Norquist’s anti-tax pledge would not dictate the GOP’s strategy on the fiscal cliff, raising questions across Washington about whether Norquist’s ironclad hold on the Republican Party has loosened.

Norquist, a zealous, self-promoting Washington icon who ­presides over a weekly meeting of top conservative players, has quietly amassed an extraordinary amount of power in the Republican Party without ever being elected to office. The 56-year-old president of Americans for Tax Reform is a former Reagan-era operative who launched his pledge in 1986, wheedling and cajoling so many GOP lawmakers into signing it over the years that it has become a Republican rite of passage. He keeps the source of his power, the original signed pledges, in a secret fireproof safe.

But now some Republicans are openly pining for the days when Norquist’s specter didn’t loom over their budget dealings. Among them is strategist John Weaver, a former top adviser to Sen. John McCain (Ariz.) and moderate 2012 presidential candidate Jon Huntsman Jr.

“The party and conservative movement will no longer be held hostage by a Washington, D.C., lobbyist,” Weaver said. “Obviously the party will always be the one standing for lower tax rates and more efficient government, but to compete for the right to govern nationally, party leaders must — and ultimately will — act responsibly.”

This is well-worn territory for Norquist. Every time there is discussion about Republicans voting for a tax increase, his influence on the party is called into question — and somehow his influence has continued and even grown.

But the scenario seems a little different this time; this challenge to Norquist’s anti-tax orthodoxy has been building for a while. Some Republicans have been toying with the idea of making increased tax revenue part of a deficit-taming deal for more than a year. Higher taxes were a component of the framework outlined by the bipartisan fiscal commission chaired by Erskine Bowles and Alan Simpson, and they were included in secret bipartisan Senate talks led by the “Gang of Six.”

Those voices mounted after the messy debate in the summer of 2011 over raising the nation’s debt ceiling, a consumer-confidence-shaking budget showdown that many Americans, according to polls, blamed on GOP intransigence.

Even House Speaker John A. Boehner (R-Ohio) expressed dismay with Norquist’s pledge and his role in the GOP at the time. Asked a year ago whether Norquist was a positive influence on the party, Boehner offered an unusually stern retort.

“It’s not often I’m asked about some random person in America,” he said, referring to Norquist.

Last November, 100 House members, 40 of them Republicans, wrote a letter to Congress’s deficit-reduction “supercommittee” urging it to consider all options — a vague pronouncement that, at least in theory, endorsed tax increases forbidden by Norquist. A number of House members, including freshman Rep. Scott Rigell (R-Va.), said openly that they no longer felt bound by the pledge they had signed when running for office. Rigell was reelected this month.two new grafs for su

The shift has been encouraged by Democrats, who have worked to make Norquist the face of GOP obstruction. Week after week, Democratic leaders have bashed Republicans for pledging fealty to Norquist rather than working independently to broker deals.

And now, with severe cuts in line if Congress doesn’t reach a deal on the fiscal cliff, coming to an agreement is paramount. Analysts have a hard time forecasting a deal that doesn’t include tax increases — especially after President Obama won reelection, having run in large part on letting tax cuts for the wealthy expire.

Some Republicans are bowing to that version of reality. Over the weekend and on Monday, Sens. Lindsey O. Graham (S.C.), Saxby Chambliss (Ga.) and Corker (Tenn.), along with Rep. Peter T. King (N.Y.), said they would be willing to violate the pledge under the right circumstances.

Boehner has also said that revenue increases will be on the table, though he has focused on closing loopholes rather than raising tax rates.

And on Monday, Sen. Lamar Alexander (R-Tenn.) brushed off Norquist’s influence while saying that only Obama’s leadership can clinch a deal. “I’ve only taken one oath,” Alexander told reporters, referring to his oath of office.

He noted that top congressional Republicans have publicly expressed willingness to increase tax revenue — making a subtle shift in tone without actually embracing higher tax rates. “I think Republicans have done plenty of talking about revenues on the table,” Alexander added, suggesting that Obama needs to do the same in embracing entitlement cuts. “We’re ready. It’s time for the president to step up.”

Other conservative voices, including former Florida governor Jeb Bush and commentator Bill Kristol, have expressed opposition to Norquist’s pledge recently. And a surprisingly high number of GOP congressional candidates this year declined to sign it.

Whether they support closing loopholes or raising tax rates, as long as those revenue increases aren’t offset by other revenue cuts, Republicans who vote for the package will be in violation of the pledge — and it’s harder and harder to conceive of a deal getting done without this happening.

Norquist, for his part, says he is confident that the pledge will remain unbroken. He noted that Graham, Corker, Chambliss and King have all flirted with revenue increases in the past, as have some other Republicans, but that Republicans haven’t voted for a tax increase since the early 1990s.

“Do I think everyone’s abandoning the pledge? No. I didn’t then, and I don’t now,” Norquist said in an interview Sunday. “I don’t think between now and 2014 that either the South Carolina senator [Graham] or the Georgia senator [Chambliss] will vote for a tax increase.”

Norquist continued in that vein in an interview with CNN on Monday morning, dismissing the chatter: “We’ve got some people discussing impure thoughts on national television.”

If the pledge is broken, though, it will probably take a year or two to evaluate Norquist’s remaining political capital. That’s when Republicans in Congress will face reelection.

The real peril would appear to be in the primaries, where anti-tax tea party candidates have upended a number of moderate and establishment candidates in the past two elections. If the pledge is broken, it will fall to its supporters to make those who broke it pay a political price. Otherwise, Republicans will have little incentive to abide by it in the future.

Graham happens to be a top target of the conservative base in 2014, and Chambliss is being eyed by some potentially formidable GOP opponents, including former Georgia secretary of state Karen Handel.

Norquist doesn’t recruit and support primary challengers, but he has great influence on conservative groups that do.

“We would certainly highlight who has kept their commitment and who hasn’t,” he said Monday.

So far, the tea party community and fiscally conservative groups have been conspicuously quiet when it comes to potential breaches of the Norquist pledge. But that could change quickly if conservatives view a deal poorly.

GOP strategist Ed Rogers noted that the party paid a price for raising taxes in George H.W. Bush’s administration and would do so again if it raised taxes now.

But even if Republicans desert the pledge this time, he said, Norquist will be here to stay.

“As long as he wants to be, Grover is influential,” Rogers said. “He’s got a big intellectual and policy foothold in this party.”