For decades, the Americans for Tax Reform founder has locked in lawmakers to oppose new taxes. The deficit debate is his greatest triumph—and biggest test

A "campaign promise" is not exactly an oxymoron, but of all the pledges a person can make—wedding vow, blood oath, playground pinkie swear—it's the least dependable. Promises made with certainty a dozen times a day on the stump rarely survive their collision with the complications of actual governing. Ronald Reagan promised to slash the federal budget deficit. George W. Bush promised not to get involved in nation-building abroad. Barack Obama promised to close Guantanamo in his first year in office. They all sounded pretty good at the time.

Recent American politics has had one remarkable exception to the rule: the Taxpayer Protection Pledge. Administered by the Washington-based Americans for Tax Reform and created by the organization's founder, Grover Norquist, the pledge binds its takers to oppose "any and all efforts" to increase marginal income tax rates and to protect tax deductions and credits. Two hundred thirty-three of the 240 House Republicans have signed it, as have 40 of the 47 Republican senators. Two House Democrats and one Senate Democrat, Ben Nelson of Nebraska, are signatories, as well as 1,252 state legislators who signed a less specific pledge. All of which would be meaningless without theomertà-like fidelity with which pledge takers stick to their vows once in office. Any time a proposal is floated to increase taxes in any way—not just income taxes or trimming tax credits, but capital-gains taxes and even excise taxes on gasoline or tobacco—it's a safe bet that Norquist's army will line up against it.

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This moment is a triumph for the 54-year-old Norquist, too. For decades he's worked Congress and cable news studios to promote his single issue, promoting those who sign his pledge and punishing those who even consider breaking it. "He's a little bit like the old Roman emperor, turning the thumbs up and thumbs down," says Bruce Bartlett, a domestic policy adviser and Treasury official during the Reagan and George H.W. Bush Administrations. "He has an enormous amount of power, more than he's ever had before."

Yet even as it demonstrates Norquist's power, the budget crisis threatens to undermine him. In recent weeks, Norquist and his organization have engaged in a very public dispute with Dr. Tom A. Coburn (R-Okla.), perhaps the most uncompromising spending hawk in the U.S. Senate, over the senator's willingness to entertain tax revenue increases—not rate hikes, but the elimination of certain deductions and tax credits—as part of the so-called Gang of Six deficit deal. Coburn and GOP colleagues Saxby Chambliss of Georgia and Mike Crapo of Idaho have been negotiating with Senate Democrats on a potential compromise, and they have argued that the yawning budget gap is impossible to close with spending cuts alone. To Norquist, entertaining the idea of a tax increase at the very moment when the deficit is forcing Democrats to consider deep spending cuts is snatching defeat from the jaws of political victory. Who wins the argument will determine whether the current deficit debate is the apotheosis of Norquist and his pledge or the moment their influence begins to wane.