For years, advocates of supply-side economics have justified repeated calls for tax cuts for high earners by arguing the cuts will pay for themselves by dramatically boosting economic growth and thus tax revenues. They have just as adamantly insisted that if only Capitol Hill's official arbiter of the budgets, the Congressional Budget Office, would evaluate tax cuts through the prism of "dynamic scoring" -- which projects the macroeconomic impact of tax cuts as well as the lost revenues they produce -- their point of view would be vindicated.

Well, CBO has done just that with President Bush's budget, and guess what? In a report prepared under the supervision of a supply-side economist handpicked by the White House and published last week, CBO concluded the president's budget would make long-term budget deficits worse rather than better.

It's taking a while to sink in, but that CBO document pretty much pronounced the death of the supply-side economics.

In an irony as rich as any tax-cut beneficiary, the first publication to really explain the report's significance was the Wall Street Journal, whose editorial page has long been the Pravda of supply-siders, and the source of dozens of columns and editorials demanding dynamic scoring to reflect the "true" impact of big tax cuts. The headline over a column by Journal columnist (and CNBC Washington Bureau Chief) Alan Murray says it all: "'Dynamic Scoring' Finally Ends Debate on Taxes, Revenue."

"Do tax cuts pay for themselves?" Murray asks. "That's been the hot debate of American political economy for the better part of three decades. But it ended last week -- with a whimper." As Murray explains the CBO report, "The results: Some provisions of the president's plan would speed up the economy; others would slow it down. Using some models, the plan would reduce the budget deficit from what it otherwise would have been; using others, it would widen the deficit. But in every case, the effects are relatively small. And in no case does Mr. Bush's tax cut come close to paying for itself over the next 10 years."

This comes as no surprise to the vast majority of mainstream economists, who have always treated supply-side claims with disdain, as representing one of those "free lunch" propositions that make sense mostly to politicians.

But for Republican politicians, the supply-side pitch has become the last-ditch argument for the huge, serial, high-end tax cuts that are in turn the centerpiece of the Bush Administration's domestic policy. That happened the moment budget surpluses turned into deficits, making the GOP's original "refund" argument for big tax cuts inoperative.

So far, there's no sign the administration or congressional Republicans have taken notice of the death of supply-side economics. They're still pushing for a big new round of tax cuts targeted to the top of the income scale, and still pretending that will simultaneously set off an economic revival and erase all the budgetary red ink they've spilled in the last two years. And maybe they'll just stay in denial perpetually, repeating the ritual supply-side incantations as though they represented a living set of beliefs.

The only other rationale for perpetual tax cuts that has not already been invalidated by fiscal or economic reality is the "starve the beast" theory that cutting taxes and producing big budget deficits will eventually lead to the devastation of federal investments and programs that Republicans don't have the political courage to propose cutting outright -- a sort of gutless Gingrichism. That may actually be the real motivation for Republican fiscal policies, but it's sure to be a loser with the American public.

So supply-side economics may have died a timely death. But don't hold your breath until the failed faith's congregation sings a requiem and finds a new church.