Paul Krugman has the right of it: Few people do understand debt.
The United States emerged from World War II with a debt-to-GDP ratio of nearly 120%. On a bipartisan basis, Congress and the presidency reduced that figure to just over 30% by 1980, even federal budgets added to the gross debt. In effect, the country used debt to finance growth. (For those who believe that the government should be run like a business, leveraging growth with debt is an elementary principle of finance.) For those years in which one party controlled both the executive and legislative branches, Democrats outperformed Republicans, but reducing the ratio was fundamentally a bipartisan effort.
In 1981, the Reagan administration lowered taxes -- especially for the upper brackets -- while increasing defense spending. Although this provided a massive economic stimulus, it also initiated the long march toward our current dilemma: By the end of Bush I, the debt-to-GDP ratio increased to over 60%.
A strong economy combined with an increase in the upper brackets and a respite in medical inflation brought the ratio under 60% by the close of 2000. However, the Bush II policies (tax cuts, unfunded wars, unfunded Medicare Part D, TARP) and a mediocre economy raised the ratio from 56% to 84% by the time Barack Obama took office, a nearly incomprehensible display of fiscal incompetence and irresponsibility. Faced with a recession, Obama had little choice but to stimulate the economy. By the end of 2010, the debt-to-GDP ratio was 92%.
As Krugman points out, this doesn't necessarily put the United States in danger of becoming a net debtor: After all, we pretty much owe the money to ourselves. Plus, a recession marked by near-zero interest rates makes for a good time to borrow and further stimulate the economy. It is a notably bad time to introduce austerity measures (see Europe, Derangement of).
Our debt "crisis," such as it is, is a long-term problem that can be addressed by a recovering economy and a return to pre-Bush II upper tax brackets. Elimination of the entire Bush tax cuts would have even greater effect, but, given the ongoing contraction of the middle class, it hardly seems right to pile on.