I was under the impression Buchanan was more incompetent than anything. I would have to say Woodrow Wilson. U.S. involvement in WWI, censorship, federal income tax, federal reserve, segregation of the military, Espionage Act 1917, Sedition Act 1918, segregation of federal government, influence in South America, Treaty of Versailles, etc. FDR and Bush are probably close seconds. I haven't been a fan of Obama, but I don't think he has done enough to name him the worst all time. Certainly has the potential though.