The biggest trade deficit is with China, too, at $162 billion. Japan is next, at $75 billion.

In a very real sense, the U.S. economy is dependent on the central banks of Japan, China and other nations to invest in U.S. Treasuries and keep American interest rates down. The low rates here keep American consumers buying imported goods.

But the lack of fiscal discipline in the United States is undermining the value of the American dollar, thereby lowering the value of the U.S. Treasuries in foreign banks. As the dollar's value drops, other nations' willingness to keep investing cannot last, says Nouriel Roubini, an economics professor at New York University.

If those banks reduced their dollar holdings or were simply less willing to invest so much, it could spark a sharp fall in the value of the dollar. And that could create a host of economic problems.

Economists and business leaders are closely watching China's decision last month to uncouple the value of its currency, the yuan, from the dollar and tie it instead to a basket of different currencies. The move could make the dollar's position less exposed to a quick shift by international investors — or it could spur those investors to look elsewhere and leave the United States' position more precarious.

What if . . .

In the end, Roubini, Walker and others say, disaster is still avoidable, but it's going to require the American people and the country's leaders to clean financial house — to reduce the federal deficit and the trade deficit. Global economics may drive some changes: if Japanese cars cost more, for example, Americans may buy less-expensive GMs.

If not, the future poses some frightening what-ifs:

• What if the dollar plummets? Do stocks follow? How about pensions?

• What if interest rates soar? How would all the new homeowners, who stretched to buy with adjustable and interest-only loans, cover their mortgages?

• How would consumers with record credit-card debt make their payments? Would they stop buying? Stop taking vacations? What will happen if they go bankrupt? New rules going into effect later this year make it harder on such debtors.

• How would government, which depends on the taxes of a strong economy to operate, keep all its promises?

Roubini says time is critical because the worse debt becomes, the more vulnerable America is to shocks in the global economic systems — another spike in oil prices, another major terrorist attack, another major military conflict.

OK, now back to you. No one's asking you to write a check to cover that $145,000, not yet. But the pressures are building around the world, in Washington and in America's homes to straighten out our finances or get ready for a real mess.

"We're living beyond our means," Roubini says, "and we have to get our act together."

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NEXT: Doomsday scenarios in which debt could derail the economy.