anonymous user 188.8.131.52 (Midian?) asks: Why focus on the President? It is US Congress that controls the purse strings. Try an accurate comparison, compare control of Congress, not Presidential party.
I got the best data I could find quickly, which wasn't much, and did a File:US public debt by party.ods showing year-by-year changes to the national debt along with what party was in control of Congress at the time. As far as I can tell there's no correlation; this might be explained by the fact that the President ultimately can veto any budget he doesn't like... or possibly better data is needed. (Normalizing the deficit by showing it as a fraction of GDP would be a good start.)
Still, the data for presidents vs. deficit is pretty clear. (Text in that graph suggests further data sources which might have better data for this graph, however.)
--Woozle 14:00, 19 November 2009 (UTC)