Krugman and other Democratic loyalists are forever pointing out that the national debt was a much higher percentage of GDP at the end of World War II and therefore we should not be concerned about the high debt levels of the present day. These arguments are completely disingenuous.
During World War II, America mobilized a huge effort to produce guns, tanks, aircraft and other war-related goods. When the war ended, there was no longer a need for all of this spending and spending levels were dramatically reduced almost overnight. There were no "hard decisions" about reducing spending. The war was over.
Today, spending is driven by entitlement programs that large parts of the American public depend upon and expect to see continued. Spending, long run, can only be reduced by essentially eliminating these entitlement programs -- restraining them won't work for the same reasons that they have never been restrained.
Both federal and state spending is mostly driven by entitlements. It isn't fraud and "wasteful" spending. It is the entitlements. It is not the war in Iraq and the war in Afghanistan. It is the entitlements.
So, unless Krugman and his loyalist band of the Democratic faithful are proposing massive cuts in entitlement spending, which last I checked they weren't, America faces a massive debt crisis that will, in the end, require the same solution that Europe is now moving toward -- eliminate the entitlements.