The basis for much of Herman Cain’s presidential campaign is what he calls the “9-9-9” economic plan. It’s basically Cain’s approach to tax policy, in which he envisions a system with a 9% income tax, a 9% corporate tax, and a 9% sales tax. The cast of “Fox & Friends” just loves the idea.

The plan hasn’t been subjected to much scrutiny, in part because Cain isn’t seen as a credible challenger, but so long as he’s rising in the polls, it’s worth taking a moment to give this idea a quick look.

The obvious problem, of course, is that tax rates this low simply won’t generate a sufficient amount of funds. In short, Cain’s numbers don’t add up. If the country were to adopt 9-9-9, the prospect of reducing the debt would disappear, and much of the federal government would have to be dismantled. Perhaps that’s the idea — in a feature-not-a-bug sort of way — but it’s not going to happen. Cain is selling a pipe dream.

But that’s only part of the problem. Fox’s Chris Wallace asked Cain the other day about 9-9-9 simply turning into 12-12-12 as fiscal requirements grow. The Republican candidate said he wouldn’t allow that: “In the legislation that I’m going to ask Congress to send me, I want a two-thirds vote required by the Senate in order for them to change it. That will impede cavalierly raising it.”

As Paul Waldman explained yesterday, that’s quite nutty.

[T]his sounds like a great precedent. Why didn’t every previous president think of that? Whenever a bill you support is ready to be passed, insert a provision demanding a supermajority to undo it. And why stop at 2/3? Why not have a 9/10 supermajority requirement, or a 99/100, or just go all the way and legislate that changing your legislation will require a 100-0 vote in the Senate and a 435-0 vote in the House?

Exactly. I’m sure every president in history would have loved to include provisions in preferred legislation making it nearly impossible for future policymakers to change their handiwork. Our system of government, though, doesn’t work that way.

Cain apparently doesn’t know that, but he should. In some circles, voters are impressed by political candidates who run without any experience in or knowledge of American civics, but that’s a shame. Had Cain ever held any public office at any level, he might understand what is and isn’t possible.

Steve Benen

Follow Steve on Twitter @stevebenen. Steve Benen is a producer at MSNBC's The Rachel Maddow Show. He was the principal contributor to the Washington Monthly's Political Animal blog from August 2008 until January 2012.