You know what they say about living by the sword.

In politics, the same goes for polls.

As Rick Perry realized when the mere prospect of his entrance into the 2012 Republican presidential race made him an automatic frontrunner immediately following the announcement of his candidacy, polls are flattering. In Perry’s case, the polls proved to the pundits and the naysayers that he could be a contender, that he could win the GOP nomination, and that people liked him – or at least that they liked him more than they like the other guy, which, in the GOP primary race, actually meant that they didn’t dislike him as much as they disliked the other guy.

And then the polls suddenly proved the opposite.

Once the media sinks its talons into a candidate, which is what happens when public opinion polls show him or her as a potential frontrunner, every aspect of his private and public life is opened up to mass dissection, dissemination, speculation and criticism. Every piece of legislation he backed, every gaffe or false statement he makes, every twitch, stutter and scratch goes instantly viral.

It happened to Perry. It happened to Michele Bachmann when she was briefly considered a contender in the 2012 Republican presidential race, and it’s what is now happening with Herman Cain, whose straw poll victory in Florida turned him into a top-tier candidate almost overnight.

Cain went from being ignored by both the media and the other candidates to being an instant political celebrity. Needless to say, the scrutiny hasn’t done him any favors.

Not only has he caught fire for his opinions about Muslims, his claim that poor people should blame themselves for not being rich, and his statement that the United States should build an electric fence along its border with Mexico, the last week of Cain news coverage centered on the heart of the pizza executive’s campaign platform – his signature 9-9-9 tax proposal.

During the GOP debate in Nevada Tuesday night, the 9-9-9 plan was eviscerated by every candidate on stage, from the frontrunner on down.

Perry’s response was unlike his other comments throughout the debate – and by that I mean coherent.

“Herman,” he said, “I love ya brother, but let me tell you somethin’. You don’t have to have a big analysis to figure this out. Go to New Hampshire where they don’t have a sales tax, and you’re fixin’ to give ’em one. They’re not interested in 9-9-9.”

Rick Santorum, in his usual “family values” pitch, said he opposed the 9-9-9 plan essentially because it didn’t do anything to encourage married couples to have children.

Bachmann, who had inferred during the last debate that the 9-9-9 plan was satanic, said Tuesday night that she opposed the proposal because it would give Congress a 9-percent sales tax, and “how long will it take a liberal president and a liberal congress to run that up to maybe 90 percent? Who knows?” (A technicality here: If Cain were elected president – the only chance the 9-9-9 plan would have of becoming a national policy – there wouldn’t be a “liberal president” in office.)

Ron Paul said “the worst part about” the 9-9-9 plan is that “it’s regressive.”

“A lot of people aren’t paying any taxes,” Paul said, “and I like that. (But) I don’t think we should even things up by raising taxes. So it is a regressive tax, so it’s very very dangerous.”

Try as he may, Cain just couldn’t convince anyone on the stage that the independent analysts who said his plan would raise taxes on 84 percent of households were wrong. As evidence of his distinguished colleagues’ ignorance, Cain relied on a rather interesting cliché.

“This is an example of mixing apples and oranges,” he said. “The state tax is an apple. We are replacing the current tax code with oranges. So it’s not correct to mix apples in oranges.”

“Once again, unfortunately,” he said at another point in the debate, “none of my distinguished colleagues who have attacked me tonight understand the plan… It’s apples and oranges.”

Mitt Romney, the currently frontrunner, asked Cain, “Herman, are you saying that the state taxes will also go away?”

“No,” Cain replied. “That’s an apple. We’re replacing a bunch of oranges.”

“So, then Gov. Perry was right?”

“No,” Cain said. “He wasn’t. He was mixing apples and oranges.”

Obviously amused, Romney asked, “Well but, will the people in Nevada not have to pay a Nevada sales tax and in addition pay the 9 percent sales tax?”

“Governor Romney,” Cain said, as annoyed as the rest of the field was entertained, “you’re doing the same thing they’re doing. You’re mixing apples and oranges. You’re going to pay the state sales tax no matter what. Whether you throw out the existing code and you put in our plan, you’re still going to pay that…That’s apples and oranges.”

“Right,” Romney replied, “and I’m going to get a bushel basket that has apples and oranges in it, because I’m going to pay both taxes, and the people of Nevada are going to pay both taxes.”

Moderator Anderson Cooper then put the question to Newt Gingrich: “Speaker Gingrich, you have said in recent days that Cain’s 9-9-9 plan would be a harder sell than he lets on. How so?”

“Well,” Gingrich said, “you just watched it.”

Before the debate began, L.A. Times reporter Michael Hiltzik wrote that “Herman Cain’s 9-9-9 plan would probably be seen as just another cockamamie tax scheme were it not for his surprising ascendance to front-runner ranks in the Republican Party primary. Yet one of the more interesting questions raised by the plan hasn’t gotten much attention: What accounts for the enduring popularity of such tax nostrums, when they never pencil out?”

A few hours later, Hiltzik  got his answer when “the enduring popularity” of 9-9-9 met Earth.

Has the Cain poll bubble burst?