Second, the maturity profile of most countries' marketable government debt is relatively short: over half of America's and more than 40% of that of Germany, France and Italy matures within three years.

ECONOMIST: Economics focus

Now, as the baby boomers' promised benefits swamp the payroll-tax collections from today's workers, the government has to swap the trust funds' nonmarketable securities for marketable Treasury debt.

WSJ: Cox and Archer: Why $16 Trillion Only Hints at the True U.S. Debt