(FORTUNE Magazine) – After four fat years in which the U.S. government took in more than it spent, the big, bad budget deficit is back: The U.S. is likely to spend at least $100 billion more than it takes in in fiscal 2002. Many politicians and pundits--mostly Democrats--are loudly bemoaning the turnabout, which the more intemperate are already calling a National Tragedy. Others--mostly Republicans--are saying it's not such a big deal.

Who's right? The answer depends on how you look at three questions.

Question No. 1: What caused it? The answer: Shit happens.

George Bush's detractors are blaming the deficit on last year's $1.2 trillion, ten-year tax cut, and they will keep saying that so often and so volubly that six months from now most people will probably believe it.

But it's not true. Back in May, before the tax plan was enacted, the Congressional Budget Office predicted that the federal budget would produce a surplus of $304 billion in 2002. In its August update--after the tax plan had become law--the CBO was still predicting a surplus of $176 billion. The CBO attributed only 30% of the downward revision to the tax cuts; the rest was due to lowered economic expectations, other spending, and technical revisions.

Had the economy narrowly avoided a recession, as the CBO and most private-sector forecasters thought likely, there would have been no budget deficit in 2002. Nothing about the Bush tax cuts has changed in the meantime. What's changed, of course, is the economic outlook--which was worse than anyone thought, and then worsened a lot more as a result of the terrorist attacks of Sept. 11--and the growth rate of federal spending, which has increased sharply.

Had there been no tax cuts, the deterioration of the economy and the spending increases wrought by the terrorist attacks would have produced a deficit anyway. A smaller deficit, yes. But a deficit nevertheless.

Question No. 2: Should we be worried about this year's deficit, or the likelihood that the budget will be in deficit for another year or two? The answer is no.

During recessions the U.S. budget typically goes into deficit as incomes and tax revenues fall and government expenditures rise. Most economists think that's a good thing. To increase taxes or cut spending to balance the budget would further weaken the economy, either prolonging the recession or slowing the recovery. The kinds of budget deficits we're talking about now--$100 billion, these days less than 1% of GDP--are simply not worrisome from an economic perspective. (If you make $85,000 per year and something happens that causes you to borrow $850, do you panic?) Or think of it this way: The year after the last recession, the budget deficit rose to $290 billion--4.6% of GDP.

Ditto for wars. The U.S. has gone into hock during every war it has fought. During World War II--to pick the most extreme example--the budget deficit exceeded 20% of GDP for several years.

Nobody, in fact, is arguing that we increase taxes right now to balance the budget. Hardly anybody is arguing that we rescind the planned Bush tax cuts, since all but the most unreconstructed liberals understand that even that would have a negative economic effect. Individuals and businesses act differently today if they know their taxes will be higher or lower in the future.

Question No. 3: Does the deficit raise long-term concerns? The answer is yes. Looking again at the pre-Sept. 11 projections, the CBO estimated that the total surplus for 2002-11--after including the effects of the tax cuts--would be $3.4 trillion, down from a projected $5.6 trillion before the cuts. What the Bush plan did was to wipe out most of the ten-year surpluses for everything except Social Security. This means that Democrats and Republicans alike will need to make hard choices once the recession ends. Some of the costs associated with new defense and homeland security initiatives will surely be permanent, so unless we want to raid the Social Security trust funds, we will have to either raise taxes or cut other spending to make up the shortfall.

So expect a return to the kind of fiscal-policy political trench warfare that took place in the 1980s and early 1990s. Some people may consider that a national tragedy; a better way to look at it is as an opportunity for a worthwhile debate about the nation's tax and spending priorities.

ROB NORTON, a former FORTUNE executive editor, is a freelance writer, editor, and consultant in New York City. He can be reached at rob@robnorton.com.