Dr. Mike Walden, North Carolina Cooperative Extension economist in the College of Agriculture and Life Sciences at N.C. State University, responds:

"No, there's a whole other part called unfunded liabilities that you may want to add to that $10 trillion. Unfunded liabilities are primarily related to Social Security and Medicare. What economists do is they sit down and say, 'Alright, let's try to project how much we're going to spend over the next x years, say 40 years, on Social Security and Medicare.' And we can do that by looking at demographics and numbers of people, etc., etc. Then let's calculate how much in tax revenues are going to be raised for those two programs, and if they match, then we don't have a problem. But if there's a gap - that is, if the expected amount of spending is going to be greater than the expected amount of revenue, then we do have a gap, and we actually call that gap unfunded liabilities. Well, the economists who have done this, unfortunately, find there's a gap. And the gap is a big one. It's in the range of $30 to $50 trillion. And of course, this is related to the fact that we are an aging society - the fastest-growing demographic group is over 65, a lot of medical expenses there. So yes, it's certainly right to worry about that $10 trillion, but an even bigger problem is this unfunded liability part of $30 to $50 trillion and how that gap might be filled."