Paul Krugman: How big is $9 trillion?

... Right now, federal debt is about 50% of GDP. So even if we do run these deficits, federal debt as a share of GDP will be substantially less than it was at the end of World War II. It will also be substantially less than, say, debt in several European countries in the mid to late 1990s. (There are some technical issues in comparing these various numbers — gross debt versus net (mainly about Social Security) and overall government debt versus federal, but they don’t change the basic picture.)

Again, the debt outlook is bad. But we’re not looking at something inconceivable, impossible to deal with; we’re looking at debt levels that a number of advanced countries, the US included, have had in the past, and dealt with.