David Letterman grilled Republican presidential candidate Herman Cain on his 9-9-9 tax plan during the tapping of the "Late Show with David Letterman."
"You don't even know what it means. I heard somebody say to you, 'so how would so-and-so and so-and-so be handled under 9-9-9' and you said, 'I don't know!'' Letterman said.
"That was one of those obscure questions that was asked about 9-9-9," responded Cain.
"Yeah, but you've got to deal with the obscurity when you're president," Letterman said.
Cain, the former Godfather's Pizza CEO, defended his tax plan, saying his proposal is bold and will help create jobs.
Letterman joked that the title of Cain's economic plan appears to be a toll free number.
"You dial 9-9-9, you get a free pizza," Letterman said.
"Instead of a free pizza, when you dial 9-9-9, you're going to be able to get a job," Cain retorted.
Cain's interview airs Friday.
