I'm sure there was some silly stat about Presidents being assainated or dying in office every 20 years or something? Reagan defied it, even though he was shot. Bush would be the next in line, and lets be honest, there can be few Presidents in history who'd be capable of generating a suspect/ motive list the length that he's built up.
Bush 2007? - elected 2000
Reagan (1981? near miss) - elected 1980 - 18 yrs
Kennedy 1963 (ass) - elected 1960 - 18 yrs
Roosevelt 1945 (d in office) - elected 1933 - 18 yrs
Harding 1923 (d in office) - elected 1921 - 22 yrs
McKinlay 1901 (ass) - elected 1897 - 22 yrs
Garfield 1881 (ass) - elected 1881 - 20 yrs
Lincoln 1865 (ass) - elected 1861 - 16 yrs
Taylor 1850 (d in office) - elected 1849 - 15 yrs
Harrison 1841 (d in office) - elected 1841 - 9 yrs
Nah.....Its complete cobblers

Mind you with a 23% fall out rate its got to be statistically one of the most hazardous jobs in the world. Dick Cheney might be worth half a point yet with number of heart attacks he seems to suffer, or is it his hunting partners who are in greater danger?