To show that the looming fiscal crisis is not a partisan issue, he brings along economists and budget analysts from across the political spectrum. In Austin, he's accompanied by Diane Lim Rogers, a liberal economist from the Brookings Institution, and Alison Acosta Fraser, director of the Roe Institute for Economic Policy Studies at the Heritage Foundation, a conservative think tank.

Their basic message is this: If the U.S. government conducts business as usual over the next few decades, a national debt that is already $8.5 trillion could reach $46 trillion or more, adjusted for inflation.

A hole that big could paralyze the U.S. economy; according to some projections, just the interest payments on a debt that big would be as much as all the taxes the government collects today.

And every year that nothing is done about it, Walker says, the problem grows by $2 trillion to $3 trillion.

People who remember Ross Perot's rants in the 1992 presidential election may think of the federal debt as a problem of the past. But it never really went away after Perot made it an issue, it only took a breather. The federal government actually produced a surplus for a few years during the 1990s, thanks to a booming economy and fiscal restraint imposed by laws that were passed early in the decade. And though the federal debt has grown in dollar terms since 2001, it hasn't grown dramatically relative to the size of the economy.

But that's about to change, thanks to the country's three big entitlement programs — Social Security, Medicaid and especially Medicare. Medicaid and Medicare have grown progressively more expensive as the cost of health care has dramatically outpaced inflation over the past 30 years, a trend that is expected to continue for at least another decade or two.

And with the first baby boomers becoming eligible for Social Security in 2008 and for Medicare in 2011, the expenses of those two programs are about to increase dramatically due to demographic pressures. People are also living longer, which makes any program that provides benefits to retirees more expensive.

Medicare already costs four times as much as it did in 1970, measured as a percentage of the nation's gross domestic product. It currently comprises 13 percent of federal spending; by 2030, the Congressional Budget Office projects it will consume nearly a quarter of the budget.

Economists Jagadeesh Gokhale of the American Enterprise Institute and Kent Smetters of the University of Pennsylvania estimate that by 2030 Medicare will be about $5 trillion in the hole, measured in 2004 dollars. By 2080, the fiscal imbalance will have risen to $25 trillion. And when you project the gap out to an infinite time horizon, it reaches $60 trillion.