All of the Republicans running for president agree: The corporate income tax needs to be sliced. The only point of dispute is how big a cleaver to wield. Mitt Romney would lower the corporate rate from 35 percent to 25 percent. Tim Pawlenty wants it down to 15 percent. Michele Bachmann scoffs at their timidity and says bring the rate down to 9 percent. At last night’s debate in Iowa, Rick Santorum pledged to zero it out for manufacturers.*

So what would a country with ultra-low corporate tax rates actually look like?

That means there’s strong agreement that the corporate tax code should be reformed. What about the sweeping cuts Republicans are demanding? “It’s true that drastically reducing the corporate tax rate would make the U.S. a more attractive place to invest — and probably turn us into a tax haven,” says Alan Auerbach, a tax expert at the University of California at Berkeley. But, he notes, how would you make up the revenue?

Right now, the corporate income tax provides about 10 percent of revenue for the federal government, although it can range pretty widely year by year. According to the Joint Committee on Taxation, every percentage-point reduction in the 35 percent corporate tax rate would mean $8 billion a year or more in foregone revenue. So Romney’s proposal would worsen the deficit by about $800 billion in the next decade. Pawlenty’s? $1.6 trillion. Bachmann’s? More than $2 trillion.

Simply slashing the corporate tax would also make the tax code considerably less progressive. As I wrote yesterday, there’s considerable debate among economists about whether the corporate income tax falls primarily on shareholders, workers or customers, but the general view is that it’s a progressive tax, falling disproportionately on richer Americans. Are there ways to alleviate that problem? Sure. “If the defense of the tax is that it falls mainly on shareholders anyway, then one thing you could to do would just be to tax shareholders directly,” says Graetz. In other words, cut the corporate income tax and raise the capital gains tax. Needless to say, none of the GOP candidates are considering anything like that.

There’s also the tax-shelter question to consider. Long ago, when income tax rates were much higher than the corporate tax rate — in 1951, for instance, the top marginal rate was 91 percent while the corporate rate was 50 percent — many Americans would simply accumulate funds inside a corporation to evade the tax. If the corporate rate was shrunk to Bachmann- or Cain-like levels, we’d likely see a repeat of that. Granted, Congress has dealt with this problem before — taxing income in corporations that wasn’t being used to finance activities, say — and, as Graetz notes, it’s no more of a headache than figuring out how to deal with, say, transfer pricing under the current corporate tax regime. But, again, it’s not something any of the Republican candidates have shown signs of thinking about.

There are also, it should be noted, alternatives to simply hacking away at rates indiscriminately. President Obama has suggested reducing the corporate tax rate while also closing many of the exemptions in the code, in order to make the whole thing flatter and revenue neutral. Not surprisingly, companies that benefit from those loopholes don’t like the idea. Alternatively, Berkeley’s Alan Auerbach has put forward a somewhat more complicated proposal [PDF] that would base the tax less on the source of income (which gives incentives for companies to shift profits abroad and shift debt to the United States) and instead focus purely on transactions taking place inside the United States. It’s not as good a sound bite as, “Let’s just zero out the corporate income tax,” but it avoids many of the downsides, too.

*Correction: This post originally stated that Herman Cain wanted to reduce the corporate income tax rate to zero. That’s incorrect. I misread his remarks from last night’s debate — he wants to bring the tax on repatriating foreign profits down to zero and reduce the corporate income tax rate down to 25 percent. Apologies for the error.