ThinkProgress has a slam dunk:

It is not true that the debt under Obama has increased more than all the other presidents combined.

When Obama took office the debt stood at $10.6 trillion. After inheriting two wars and the worst economy since the Great Depression, the debt has grown by $3.7 trillion since Obama has been in office. Palin is off by about $7 trillion.

Her publicist, Greta van Susteren, does not dispute this and does not point out that a huge amount of it is due to a collapse in revenues during a deep recession that Obama inherited – a recession that would have been even deeper were it not for the stimulus package. Now I can guess you can still argue that there should not have been a stimulus at all, but even then, who would seriously doubt that the deeper crash would have temporarily reduced revenues even further? Even the most hardcore of anti-Keynesians would acknowledge that letting the US economy hit rock bottom, and allowing the entire auto industry to be wiped out, and letting the banks collapse would have led to greater debt in the short term.

But when so many partisan hacks attacked Obama for the debt within minutes of his getting into office, who can blame this know-nothing for parroting a piece of obvious, provable untruth? And who, more to the point, will insist on a retraction? Palin doesn't do retractions. Her lies instantly become her reality.