Newly-minted GOP front-runner Herman Cain is best known for his 9-9-9 tax plan, but it turns out he opposed a key component of it — a national sales tax — less than a year ago.

In a column posted on the websites of a number of conservative publications, including The Daily Caller, Cain wrote that "the worst idea is a proposed national sales tax, which is a disguised VAT (value added tax) on top of everything we already pay in federal taxes."

A spokesman for Cain, J.D. Gordon, maintained he never opposed a national sales tax.

"The bottom line is, Mr. Cain has consistently been a supporter of the fair tax and the flat tax, and the 9-9-9 plan combines both. He has had over 500 columns posted in the past ten years and people are taking one line out of a 600-word column out of context."

The Cain campaign says that the candidate would have supported such a tax if the entire tax code would be reworked — as the 9-9-9 plan would do.

But one of Cain's reasons for opposing a national sales tax is already being used by conservatives to attack his own 9-9-9 plan — that setting the rate at 9 percent doesn't mean it won't go up in the future. Here's what Cain had to say about it:

Even worse is reason number two: In every country that has established a VAT with the promise of reducing its national debt, the VAT has eventually gone up or expanded on top of the existing tax structure. After discovering many of the tax grenades in the recently passed health care reform bill, which is already driving costs up and access down, it would be real easy for an overzealous bureaucrat to insert the language in the legislation “national retail and wholesale” tax.

Cain struggled to defend the plan under intense questioning on Meet the Press yesterday.

[h/t Sam Stein]