Updated with comments from Mitt Romney's adviser

NEW YORK ( TheStreet) -- Herman Cain's leap to a four percentage point lead in the latest NBC News/Wall Street Journal poll over the rest of the GOP presidential hopefuls comes on the heels of his clear campaign message, but until his competitors launch a sustained attack against Cain's message they should expect the former Godfather's Pizza CEO to surge.

Cain mentioned his "9-9-9" plan virtually every speaking opportunity he had at Tuesday's Republican debate , leaning heavily on the tax plan to propel his arguments.
Herman Cain finds himself leading the GOP presidential race.

Jon Huntsman and Michele Bachmann took direct aim at the plan (Huntsman made the obvious joke that he first thought the plan was a pizza deal), but neither of them offered enough quantitative criticism to override the support Cain has gained simply by spending lots of time advertising his plan.

The one candidate who seems adamant to pick apart the plan is former U.S. Sen. Rick Santorum from Pennsylvania.

Santorum, ahead of the Tuesday debate in New Hampshire, said that zero tax was better than 9%, and he took direct aim at the fact that the Granite State would suffer from Cain's 9% national sales tax.

"The last thing we need with respect to an economic plan is give the people of New Hampshire a sales tax," Santorum said Tuesday afternoon.

Santorum had a wicked smart moment that Tuesday night in New England when he singled out Cain's plan and called for a vote of hands from the Dartmouth College audience that was in attendance.

"How many people are for a sales tax in New Hampshire? Raise your hand," Santorum queried. The audience was lifeless. "There you go, Herman."

But Santorum didn't back down. After moderator Charlie Rose interrupted the former senator's shining moment, Santorum then asked the audience how many of them actually believed that Cain's 9% national income tax wouldn't be higher. Again, almost no one raised a hand.

"Herman Cain is a serious competitor, and I know that Mitt Romney respects and admires Mr. Cain," Eric Fehrnstrom, chief Romney advisor, told Fox News . "They happen to share in common the fact that they both have significant private sector experience."

But frontrunner Romney, who was the candidate that finished second to Cain in the latest poll, didn't appear to take the "9-9-9" plan seriously, as was displayed at Tuesday's debate when viewers saw the former Massachusetts governor on television laughing every time Cain shouted his tax plan's name.

What an NBC News/Wall Street Journal poll means on Oct. 13 could be worthless on Nov. 13, but Cain's rise in voter favor from 5% in August to 27% in October among the GOP field means that the underdog should probably be taken seriously by the big dogs.

But for as long as the lone gunman trying to take down Cain's campaign is Santorum, there's little reason to believe that the former pizza guy is going to falter.

-- Written by Joe Deaux in New York.

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