In a short clip previewing Friday's broadcast of the "Late Show with David Letterman," Cain, a former pizza chain magnate who is currently fighting off while enjoying a slight lead in most GOP polls, pitches the "9-9-9" proposal as an "economic growth plan," which, as he tells the host, is "bold".
"I know it's bold," Letterman says, interrupting the oft-repeated sales pitch midstream, "but you don't even know what it means."
Letterman references an instance when Cain was asked to explain how the flat tax plan would impact people in a given set of economic circumstances, which he could not readily do.
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"That was one of those obscure questions that was asked," replied Cain with a broad smile, only to be interrupted again by Letterman, insisting, "but you gotta deal with the obscurity when you're president."
As Letterman goes on to jest that Cain should create a hotline number, whereby Americans can dial 9-9-9 to get a free pizza, the GOP contender insists that his plan "works, it works... instead of a free pizza, when you dial 9-9-9, you're gonna be able to get a job. That's the whole point."
Cain's argument is that by reducing the tax burden on corporations and the people who do the hiring in America by a mammoth sum, they will have more resources available to take on additional staff.
However, analysis from the nonpartisan Tax Policy Center found the plan would increase taxes on 84 percent of Americans, with those in the lowest income bracket hit the hardest. As he originally proposed it, some 30 million American households in the lowest income bracket, which currently pay no income tax, would have seen their rate go up by the full 9 percent.
An outcry from both his Republican rivals and Democrats prompted Cain to, saying the poorest Americans, those who live under the official poverty line, and corporations which invest in downtrodden areas, would not have to pay the 9 percent rate.
That has not quelled charge that Cain's plan would be a boon to the wealthiest Americans, while increasing the financial burden on almost everyone else.
"It will raise taxes on the poor," Roberton Williams, of the non partisan Tax Policy Center, told CBS News in October. "It will cut taxes on the rich."
All Americans would also see much higher sales tax rates, which could make them more reluctant to spend.
Tune into CBS on Friday to see Cain's full appearance on the "Late Show with David Letterman".