Incumbents have won 13 of the last 18 elections (which goes back to 1900). Losers:
1. William Howard Taft -- temperamentally unsuited to the Presidency.
2. Herbert Hoover -- messed-up economy.
3. Gerald Ford -- entered the Presidency through the back door and was barely defeated in his re-election bid.
4. Jimmy Carter -- Hard luck, bad economy and the Iranian hostage situation. Got caught in a political transition from the Sough voting Democratic as a block one last time to a norm in which the South usually voted Republican. An independent candidate drew away voters who would never have voted for Ronald Reagan.
5. George H. W. Bush -- he had no idea of what to do with the Presidency in a second term.
Heck, George W. Bush and Calvin Coolidge got re-elected despite two of the weakest Presidencies ever... Obama is a much stronger President than either of those.
Are you stupid?