While Herman Cain confidently argued in favor of his 9-9-9 plan to revamp the tax code during Tuesday night's GOP debate, there is one person who is not so sure the plan is viable -- one of Cain's own consultants.

Gary Robbins, an economist who has worked on Steve Forbes' flat-tax campaigns, told Politico on Wednesday that while the plan could theoretically work fiscally and economically, he does not think a drastic reform would be accepted by the American public anytime soon.

The problem with the big-bang changes like that, the flat tax or the fair tax, is that they are so alien to the current system that it would be a great big shock, he said.

Robbins is a paid campaign consultant who crafted the plan with Cain's Chief Economic Adviser Rob Lowrie. Lowrie himself is not a trained economist; he is a an Ohio-based wealth manager for Wells Fargo. According to Lowrie's LinkedIn profile, he received a Bachelor of Science degree in accountancy from Case Western Reserve University in 1990.

Cain name-dropped Lowrie during Tuesday night's Republican debate on economic policy, after avoiding questions from the press about who was involved in crafting the plan. In recent weeks, the 9-9-9 plan -- which would aim to create a flat national 9 percent sales tax, a 9 percent income tax and 9 percent corporate tax rate -- has been embraced by many conservatives, although some economists have pointed out it may place an unfair tax burden on the nation's poor.

Robbins was a longtime treasury department employee and in 2003 Jude Wanniski -- credited with coining the phrase supply-side economics -- wrote in a Washington Times op-ed that Robbins is arguably the most respected of all supply-side tax experts.

However, while Robbins praised the philosophy behind Cain's 9-9-9 plan, he also took steps to distance himself from it in the Politico interview.

It's not a plan that I concocted, Robbins said. There's nothing wrong with the plan, it just wouldn't be the one I picked.