Almost every nation has a value-added tax (VAT), which is a type of national sales tax that is imposed at each stage of the production process. Indeed, the United States is the only developed nation without a VAT. But this is a good thing. It is no coincidence that the burden of government in America is smaller than it is in almost every other industrialized country. Simply stated, VATs are “money machines” for big government.

Not surprisingly, this is why many politicians in Washington would love a VAT. But what is surprising is that some otherwise sensible people are sympathetic to a VAT because they think it will help exports. They point out, quite correctly, that the World Trade Organization allows governments to provide rebates for value-added taxes on exports (a practice known as border adjustability). But they are wrong when they argue that this boosts exports and creates a trade advantage.

Regarding the first point, it is downright silly to argue that imposing a VAT - and then creating an export exemption - will boost exports. At the risk of stating the obvious, the export exemption cancels the tax, so the price of American products sold outside US borders would not change.

It is also misguided to claim that a border-adjustable VAT gives other nations some sort of trade advantage. Under current law, all goods sold in America, whether made in America or made in Europe, are sold without a VAT. Likewise, all goods sold in Europe, whether made in America or made in Europe, are sold with a VAT. How much more level can the playing field get? This is not just a debate for navel-gazing academics and lint-covered policy wonks. As reported by the Wall Street Journal, some Republican presidential candidates (or at least their advisers) are focused on “border adjustability.”

Mr. Thompson’s aides outline a change to the tax code that would move away from taxing income or profits and shift toward a system that would reduce taxes on exports when they cross the border and impose them on imports when they enter the country. Under international rules, the European value-added tax, a kind of sales tax, is waived for exports, but those rules block the U.S. from reducing corporate-profit taxes for exporters. “The best thing to do would be to have the [World Trade Organization] change its rules to level the playing field, and that should be the first step. If that fails then we should play by the same game that everyone else plays,” said Lawrence Lindsey, Mr. Thompson’s economic adviser and former director of the National Economic Council for President Bush.

The key question, of course, is whether focusing on the unimportant issue of border adjustability leads to good policy or bad policy. Senator Thompson has made some positive noises about a wholesale replacement of our current anti-growth tax system with a consumption-base tax system like a flat tax or national sales tax. That would be great news, and it would be great news even if border adjustability led the candidate to choose a sales tax over the flat tax. What matters is not border adjustability, but that we would be getting rid of the many warts in the current tax system. But if a myopic fixation on border adjustability led a candidate to propose a VAT or other form of national sales tax without fully (and permanently) eliminating the income tax, then politicians would have an additional source of money to waste and America would be at grave risk of becoming an uncompetitive, European-style welfare state.