(FORTUNE Magazine) – YOU MIGHT ALREADY BE WONDERING who in his right mind would want the job of President. There's a bloody mess to be dealt with in Iraq, the continuing threat of al Qaeda attacks, and a federal budget that by any reasonable accounting (one that includes long-term Social Security and Medicare commitments) is tens of trillions of dollars in the hole.

But wait, it gets worse. Whoever gets the most electoral votes on Nov. 2 also faces the prospect of having to deal with a recession in the next term. Given that we had only half a recession three years ago (more on that in a moment), it's a greater threat than is generally assumed.

You will not, of course, hear any mention of this on the campaign trail. George Bush and John Kerry may not agree on much, but they are united in their conviction that the next four years will be good ones for the U.S. economy. In President Bush's case, the optimistic outlook is explicit: The budget he proposed earlier this year assumes GDP growth of 3.6% in 2005, 3.4% in 2006, 3.3% in 2007, and 3.2% in 2008. Anything less than that, and you can forget about his plans to cut the deficit in half while continuing to cut taxes. As the challenger, Kerry hasn't had to spell out his forecasts in such incriminating detail. But without sustained, strong growth, he doesn't stand a chance of meeting his commitment to fix the nation's health-care system and slash the deficit while not raising taxes on anybody who makes less than $200,000 a year.

It is of course understandable that the men who would be President don't want to muddle their speeches with talk of what they'll do when a hypothetical downturn comes. But the rest of us have no such excuse. Yes, the last two expansions lasted so long (ten years and almost eight, respectively) that it's hard to believe that only three years into the latest, we could soon face a downturn again. But the last two expansions were exceptional: the longest and third-longest ever. The three previous ones (from 1970 through 1981) lasted one year, three years, and four years, ten months. By that standard, the next recession should begin tomorrow.

Some optimists have argued that--thanks to a more adept Federal Reserve, better-developed financial markets, and a more flexible economy--recessions don't have to come along as frequently as they used to. But that's just a theory, and the reality is that what happened in 2001 was only half a recession. For American business, it was a sharp, serious downturn. Corporate earnings plummeted; capital spending took its biggest fall in decades. Millions of workers lost their jobs, and of course the stock market tanked.

But for the vast majority of America's consumers who didn't lose their jobs or go broke buying eToys stock, there was no recession in 2001. Consumer-spending growth, which in the past usually slowed to near zero (or below) in recession years, stayed at 2.5% in 2001. Consumer borrowing, which slowed sharply in past recessions, kept rising (see chart). The personal saving rate, which rose in almost every past recession, made a brief upward spike in the third quarter of 2001 but then resumed its long decline. America's current-account deficit with the rest of the world, which last reverted to a surplus during the 1990-91 recession, just kept ballooning as Americans bought cars and TVs and computers from overseas. And we all know what's been happening with housing prices.

This remarkable performance was chiefly the work of America's banks and other lenders, which kept throwing money at consumers--especially homeowners and homebuyers--at ever lower interest rates, and the Fed, which kept throwing money at the banks. Federal tax cuts helped too. As a result, the U.S avoided a Japan-style deflationary spiral. But it also avoided the tightening of belts and paying down of debt that customarily take place during a recession and lay the groundwork for a new period of growth.

Now, three years into a new expansion, American households are in hock for a record $9.7 trillion, or 84% of GDP (also a record). Meanwhile, the country's net foreign debt had grown to $2.4 trillion, another record, as of the end of 2003.

Since this debt binge began in the late 1990s, economists, journalists, and other congenital pessimists have been arguing that it will end badly. So far they've been wrong, and as a result, most forecasters no longer pay attention to debt levels when they try to guess what GDP will be next quarter or next year. But consumer spending does account for 70% of economic activity. A mere slowdown in the growth of consumer debt and consumer spending--which is what we saw during the summer months--is enough to drag growth down below economists' (and presidential candidates') projections.

It could get worse: Morgan Stanley's Stephen Roach, one of the few Wall Street economists still willing to admit to caring about current-account deficits and consumer debt, is now forecasting a 40% chance of global recession next year as high oil prices interact with the existing vulnerabilities of the world's big economies (such as America's consumer-debt overhang) to bring growth to what he calls "stall speed."

If that happens, the occupant of the White House will have to deal with an economic reality far different from that being described on the campaign trail. Stimulating the economy will be tough, because the Federal Reserve can't drive interest rates much lower than the current 1.75%, and the already huge deficit will make tax cuts or spending programs difficult. Instead of the relatively painless solutions both candidates propose now, they'll be faced with hard choices and blood, sweat, and tears. So the critical issue for voters is not so much what the candidates promise, as what they're likely to do when it turns out those promises can't be met.