With former pizza magnate Herman Cain suddenly running second to Mitt Romney in most national polls, a Cain Mutiny was as inevitable as the Iowa caucuses moving into the Christmas season.

The rebellion against Cain as a top-tier candidate was led by three lagging GOP contenders who must know that they will never be president—Rick Santorum, Michele Bachmann and Ron Paul. The occasion for the rhetorical caning of Cain by his jealous rivals was Tuesday night’s forgettable theater-in-the-round Dartmouth debate featuring the candidates all seated at the same circular table. While the debate telecast on hard-to-find Bloomberg News may have earned the lowest ratings of the primary season, the attack lines against Cain will almost certainly provide him with eventual comeuppance.

Cain, a talented motivational speaker, had sailed through the earlier debates on his charm and the aggressive touting of his 9-9-9 tax scheme. Wildly regressive and fiscally irresponsible, the Cain concoction would scrap the entire federal tax system and replace it with a 9-percent sales tax, a 9-percent flat tax and a 9-percent corporate tax. Up to now, Cain seemed too nice a guy to criticize for a tax plan that is cockamamie even by the economically dubious standards of current Republican debate.

Tuesday night, though, was Cain’s belated introduction to big-league politics. Bachmann got the ball rolling by invoking Satan’s number from the Book of Revelation: “When you take the 9-9-9 plan and you turn it upside down, I think the devil is in the details.” But in secular anti-tax New Hampshire, the words “sales tax” may be even more potent than “Satan.” That is why Santorum, who is skilled on the attack, played to the audience in the hall when he asked, “How many people here are for a sales tax in New Hampshire?” While the results of Santorum’s impromptu poll were not visible television, no one challenged Santorum’s conclusion, “There you go, Herman. That’s how many votes you’ll get in New Hampshire.”

Rick Perry is the likely beneficiary of a Cain collapse since voters intrigued by the former CEO of Godfather’s Pizza have had four years to sign on with Mitt Romney. But Perry—who has proven to be a maladroit debater both standing behind a lectern and now seated at a round table—did nothing Tuesday night to win a single new supporter. There were no glaring errors like Perry’s incoherent answer on Pakistan in the prior debate. Instead, Perry who roared into the GOP race in August with bluster and bravado once again came across as blah, bland, and boring.

Every time Mitt Romney aces another Republican debate, a new wave of fear probably wafts through the Obama White House. Romney’s rhetorically best moment came when Cain—in a strategic misjudgment—challenged the former Massachusetts governor to name all 59 separate provisions in his economic plan. Cain’s point was that 9-9-9 was as simple to remember as a pizza commercial, while Romney’s program would never fit on a bumper-sticker. With a hint of disappointment in his voice about Cain’s innocence, Romney offered this devastating response: “Herman, I have had the experience in my life of taking on some tough problems. And I must admit that simple answers are always very helpful, but oftentimes inadequate.”

To run for president—especially without any experience in elective office—requires the kind of ego that makes Donald Trump seem like a shrinking violet. Asked in the debate about reappointing Ben Bernanke, Cain like his GOP rivals balked at a second term for the Federal Reserve chairman. But Cain went further when he said, “I have already identified two candidates—which I cannot give their names—to replace Mr. Bernanke, in anticipation of having that responsibility.” There are two obvious interpretations of that megalomaniacal answer: Either Cain was bluffing to give himself a sense of gravitas or else the pizza executive actually fantasizes about appointing a Fed chairman when Bernanke’s term expires in 2014.

This was a debate in which Newt Gingrich demonstrated yet again that he is the first presidential candidate who should come equipped with his own 7-second tape delay. Asked about the Wall Street protests, the former House speaker hit the right note when he said, “Virtually every American has a reason to be angry. I think virtually every American has a reason to be worried.” But seconds later, Gingrich crossed the line of acceptable political attack when he suggested in a loathsome moment, “And if you want to put people in jail ... you ought to start with Barney Frank and Chris Dodd"—which was a reference to the authors of the Wall Street reform act.

Over the last three months, the spate of GOP debates has crowned Romney as the undisputed front-runner, consigned Bachmann to the back of the pack despite winning the Iowa Straw Poll and prompted voters to temper their initial enthusiasm about Perry. Now Cain may be the latest casualty of a modern tradition that began with Kennedy and Nixon. But Perry, armed with cash and an eagerness to spend it on attacks ads against Romney, still has the capacity to re-emerge as the one top-tier contender who is curiously debate-proof.

Walter Shapiro is a special correspondent for The New Republic. Follow him on Twitter @waltershapiroPD.