Though many have suggested Harry Truman's 1948 campaign against a "do-nothing Congress" as a model for President Obama, Brendan Nyhan points out that "the dramatic narrative of Truman's victory doesn't hold up to scrutiny."
Key difference: "Truman's comeback was fueled by 'sizzling' growth in the year before the election (the time when voters tend to most strongly reward economic improvement)... This well-timed surge in economic growth is likely to have played an important role in the success of Truman's campaign. By contrast, the International Monetary Fund just downgraded its forecast for US economic growth in 2011 and 2012 to 1.5% and 1.8%, respectively."