In science-fiction movies, no obstacle is too big to overcome. The brilliant, determined scientist finds a way to divert the asteroid before it collides with Earth.

In real life, some problems are so daunting they are ignored until the collision occurs.

The inadequacy of New Orleans's levees and the erosion of its barrier islands offer one painful example. The U.S. economy's increasing debt to the rest of the world offers another.

The U.S., a creditor country just 20 years ago, now owes the rest of the world $2.5 trillion (if you net out U.S.-owned assets abroad with foreign-owned assets in the U.S.). The U.S. this year will borrow from abroad a sum equal to 6% of its output of goods and services, more than in any year in the past 135 for which data are available.

It will do so without obvious difficulty or disruption to the global economy. Still, hardly any reputable economist, finance minister or central banker thinks the U.S. can continue indefinitely to borrow more and more. "While this benign situation could persist for some time, it will not continue forever; and finding out just when it might end is an experiment best not undertaken," the International Monetary Fund said delicately the other day.

The steps needed to wean the U.S. from growing dependence on the savings of Asians and Europeans are unappealing to both the debtors and the lenders. (Think tax increases in the U.S. and a big upward move in China's currency.) Apocalyptic predictions that this will end in a recession-provoking Category 5 crash in the U.S. dollar or an abrupt end to foreigners' appetite for U.S. debt have been wrong so far. The combination has produced complacency and denial among politicians and financial markets. Maybe this will sort itself out smoothly; maybe not.

The problem: The U.S. spends more than it earns. The country invests more than it saves. It consumes more than it makes. A lot more. The rest of the world does the opposite, exporting excess production and savings to the U.S. Even China, which has good reason to invest at home to lift living standards, sends savings to the U.S. so Americans can get cheap mortgages. This will not persist forever.

The risk: When the world economy is lopsided, something inevitably happens to right the balance. Even those who doubt this will end with a bang worry about today's trends. Gregory Mankiw, a Harvard economist who recently ended a stint as chief White House economist, predicts, "This will work out relatively benignly." Still, he adds, U.S. reliance on the savings of foreigners portends a "less prosperous future" for the U.S. Either foreigners will decide to keep more of their money, and force the U.S. to curtail the investing needed to spur future growth, or they will keep lending to the U.S., and claim an ever-greater share of future U.S. profits.

The entrails of the government statistics provide a warning. For years, the U.S. has earned a higher return on foreign factories, real estate, stocks, bonds and bank accounts it owns abroad than foreign investors have earned on much larger investments in the U.S. The U.S. is like the safe money-market fund for the rest of the world, apparently offering low, safe returns. Last year, the U.S. received $36 billion more on overseas investments than it paid out. But the surplus is shrinking largely because foreigners have been sinking so much into the U.S. economy. In the second quarter, the surplus was down to $1 billion.

Washington think-tank economist William Cline, of the Center for Global Development and the Institute for International Economics, recently had to pick a cover for his comprehensive new book, "The United States as a Debtor Nation." One idea was to put ants crawling up one side and grasshoppers down the other, a reference to Aesop's fable. That was shot down. "People thought it was termites," he says. It would have been appropriate.

The solution: Other countries need to grow faster than the U.S. so they consume more of what they make and absorb more of their own savings. A weaker dollar and stronger Chinese yuan would help. If other countries don't pick up the pace, something is bound to happen in the U.S. -- interest-rate increases, stock- or bond-market declines, an end to the housing boom or tax increases -- that will slow the U.S. economy and its demand for foreign products and savings.

We have been here before. We know what is coming, just not how and when. In the late 1980s, U.S. borrowing from abroad soared as U.S. economic growth outpaced growth overseas, a strong dollar made imports inexpensive and budget deficits widened. Then the dollar plummeted, the stock market crashed and recession curbed U.S. appetites for imports.

As Barclays Capital chief economist Laurence Kantor reminds me, only the unforeseen reunification of Germany prevented a deeper global recession; it prodded the German government into uncharacteristically stimulative fiscal policy.

Counting on a similar miracle is imprudent.

Write to David Wessel at capital@wsj.com

Commentary:
The ONLY time the WSJ cares about our debt is when money goes to people who need it, like hurricane victims or the poor. The reason is simple - hurricane relief means there's less money to give to the rich in another irresponsible tax cut.

The WSJ editorials board has supported every deficit producing tax cut in the past 25 years and it's part of the problem It lacks the intellectual and moral standing to offer solutions (much like the GOP).

In 1981 we had less than one trillion dollars of debt. Today we have almost eight trillion. The cause - tax cuts. No other generation has been as fiscally irresponsible than this one and the WSJ editorial board helped the GOP do this to us.

Finally, the US became a debtor nation in 1982, the year the Reagan tax cut became effective. If you need any more convincing that tax cuts are bad, you've been watching way too much Fox News.