Let's say the debt crisis is 100 percent a spending crisis. Let's say it's wise to extend the Bush tax cuts forever, squeeze the estate tax on inheritance, and then maybe add some additional tax cuts for small businesses and corporate income. Let's also say that by 2015 we want the government to achieve "primary balance" -- that is, we collect enough taxes to pay for all of our programs, interest not included.

The scenario above is not so dissimilar from the Republicans' stated goal. Republicans have made it clear that they want to bring down our deficits at least as aggressively as the president's plan to hit that primary balance threshold by 2015. But the GOP's fall-time manifesto, the Pledge to America, calls for 100 percent spending cuts (ie zero percent tax increases) to reach that goal. Is this possible?

The 2015 target would require spending cuts of about $255 billion. Realistically, there are tiny short-term savings in Social Security (20 percent of the budget) and Medicare and Medicaid (another 20 percent). That would concentrate most of this $255 billion snip in non-security discretionary spending. Where do you cut?

Fortunately, Michael Ettlinger and Michael Linden from the Center for American Progress looked into this question a week ago. Unfortunately, it's a painful story. Their own $255 billion chopping block includes: 75% cut in agriculture subsidies, 40% cut in federal highway and bridge funding, and 12.5% reduction in defense spending, along with a full rollback of the size of U.S. ground forces from Iraq and Afghanistan peaks.

It's difficult for me to comment on the wisdom of some of these cuts because frankly, I don't know what many of the programs do well enough to sit at a computer and decide that they'll do fine with 70 percent of their expected budget. Would the administration of foreign affairs be OK with a 15 percent cut in ambassador salaries and embassy security? Does the National Park Service really need all those administrators and visitor service people? Should the Office of Safe and Drug-Free Schools even exist?

I don't know. But those are the kind of questions that will dog a 100 percent spending-cut solution. We don't understand every last detail of the federal government's mosaic of programs, and we also don't know how the country will pay for them after they're cut or gone.

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