(FORTUNE Magazine) – There is an important question that, if asked of either presidential candidate during the upcoming debates, is guaranteed to elicit an evasive nonanswer. It goes something like this: "All the fiscal experts agree that recent tax cuts and surging pension and health-care spending will trigger wildly unsustainable deficits as the baby boom retires. The deficit explosion, they all say, will occur whether or not your announced program for the next four years is implemented. Do you have any concrete strategy for closing that fiscal gap? If so, would you share it with the American people?"

Neither of our two political parties welcomes such a question, and therein lies a tragedy. Both like to talk volubly about the taxes they will cut and the benefits they will expand--yet this is a future that will never happen. Both dread any discussion of wrenching fiscal adjustment--yet this is the future of higher taxes and pared-back programs that we actually face. All the official reports, from the Congressional Budget Office to the Fed to the IMF, keep returning to the same bottom line: The longer we put off any sacrifice, the harder will be the blow to our nation, our economy, and our lives. In fact, Democratic and Republican leaders are handling the challenge as they might an elephant in the boudoir--by pretending it isn't there and hoping no one dares mention it.

Think I'm being alarmist? With this year's record federal deficit, we are already effectively borrowing to fund all our domestic discretionary programs. By 2020 we will be borrowing to pay for our defense programs as well, since revenues by then will cover only benefit checks and interest on the national debt. For those who want the melancholy figures, the combined cash balance of Social Security and Medicare together moves from a modest annual deficit of $25 billion in 2003 to an unthinkable annual deficit of $783 billion in 2020. According to the trustees of the Social Security and Medicare systems, the present value of the future deficits in the two programs--they are, of course, unfunded deficits--has expanded alarmingly in recent years and now stands at $74 trillion, a staggering number that far exceeds our national net worth ($43 trillion). Technically, in other words, we really are bankrupt.

David Walker, comptroller general of the U.S. General Accounting Office, holds a 15-year congressional appointment and therefore is beholden to no one. His most recent budget projection shows that by 2029, the year the youngest boomer turns age 65, the federal deficit will hit an economy-shattering 14% of GDP. And this nightmare scenario is an "autopilot" projection--that is, it assumes no new programs and no rise in interest rates. "We cannot simply grow our way out of this problem," insists Walker, now a zealous and superbly informed crusader for fiscal sanity.

Both parties have good reason to hide their own complicity in steering us toward this future. In four short years a Republican administration and Congress have taken the ten-year budget outlook from plus $5 trillion to minus $5 trillion, thereby extinguishing the party's already fading reputation for fiscal stewardship. GOP leaders have pushed every deficit button they can reach--lower taxes, higher defense spending, higher benefits (including the new Medicare prescription-drug benefit), and higher discretionary spending (both war-related and not). By voiding the congressional pay-as-you-go rule, they opened the floodgates to both permanent tax cuts and permanent benefit expansions. According to the conservative Cato Institute, they have presided over a "spending explosion."

As for the Democrats, they propose to repeal only part of the Bush tax cuts (the part that goes to "the rich"--good luck!) and spend more than all of those savings on more troops for the military, a giant new health-care program, and more benefits for veterans and colleges and kids. The Democrats have seldom met an entitlement they didn't want to expand. With not a word about controlling the unsustainable costs of the current Medicare program, they mau-maued the Republicans into expanding the Medicare drug-benefit proposal into an unfunded $8 trillion burden on future taxpayers. (That's right, the officially projected liability for just this one new benefit, Medicare Part D, is roughly twice as large as our formal accumulated national debt!) And then their complaint was that the benefit didn't go far enough.

Spokespersons for both parties try to excuse this irresponsibility. Some say that these long-run budget forecasts are too "uncertain" to be taken seriously. Nonsense. The aging of America is about as close as social science ever comes to a certainty. Absent a Hollywood catastrophe--a colliding comet or an alien invasion--it will surely happen.

Others say that large budget deficits don't hurt us. But of course they do, by suppressing domestic investment and making us dangerously dependent on a floodtide of foreign borrowing. At 5.4% of GDP, our current-account deficit with other nations now far exceeds our previous borrowing high-water line--3.7% in 1987, the year of the Black Monday stock market crash. During that period the dollar also fell by a third.

Back then we called them our "twin deficits." So, should we still? Thanks to our policy-driven budget deficit (twin No. 1), the U.S. net national savings rate has dipped below 2% of national income for the first time since the early 1930s. This savings vacuum, in turn, sucks in foreign capital through our trade and services deficit (twin No. 2). When foreigners begin to tire of acquiring our dollar assets, the game will come to a sudden and perhaps calamitous end. Hopefully, by acting now on fiscal policy, we can resolve this danger on our own terms and on our own schedule. But to do that means getting our political leaders and the public educated and aroused.

To that end, I have a suggestion. Two years ago Congress and the President established a highly credible, bipartisan national commission on the collapse of the Twin Towers. The 9/11 commission's now released report is waking up the nation to what leaders of both parties have done wrong on national security--and instructing them on how they can do it right. Our political leaders should commit to appointing a similar commission on the twin deficits. Let's learn how we can do fiscal policy right. Only this time around, let's not wait until our budget and the global economy lie in a tangled wreckage. Let's issue the report and wake up the nation before the day of reckoning arrives.

PETER G. PETERSON, Secretary of Commerce during the Nixon administration, is author of Running on Empty: How the Democratic and Republican Parties Are Bankrupting Our Future and What Americans Can Do About It.