The national debt stood at nearly $10.7 trillion, of which about $4.3 trillion is owed to other government institutions, such as the Social Security trust fund. Debt held by private investors totals nearly $6.4 trillion, or a little over 40 percent of gross domestic product.
With President-elect Barack Obama considering a massive spending package aimed at pulling the nation out of recession, the national debt is projected to jump by as much as $2 trillion this year, an unprecedented increase that could test the world's appetite for financing U.S. government spending.
"When you accumulate this amount of debt that we're moving into, it's not a given that our foreign friends are going to continue on the path they've been on," said G. William Hoagland, a longtime Republican budget analyst who now serves as vice president for public policy at the health insurer Cigna. "There's going to come a time when we can't even pay the interest on the money we've borrowed. That's default."