Graphic: The U.S. debt limit's steady uphill climb

The so-called "debt ceiling" is the legal limit on how much the U.S. federal government can owe. The government expects to reach the current ceiling of $16.4 trillion early in 2013.

U.S. presidents have had a long history of seeking higher debt limits, as indicated in the charts below, which span increases in actual and inflation-adjusted figures from 1961 to 2012.