Ideology aside he ‘s the worst because he had a ton of political capital and mismanaged it, particularly in his dealings with congress. Right wrong, Bush got stuff done.
You can't take ideology out of the equation of Obama's failure. In fact, ideology is the primary reason he failed. He's a doctrinaire Marxist, who, along with his fellow travelers in Congress, attempted nothing less than the complete and utter destruction of our constitutional republic.
They alarmed the American public so badly with their headlong rush toward a Socialist "utopia", that they caused the birth of the Tea Party movement, which is rapidly bringing about their demise. Like Pandora's Box, the Tea Party movement cannot be stopped, now that it's been unleashed.
Eventually, history will record that Obama was directly responsible for shocking the American people back to their senses, which resulted in the wholesale quashing of the entire left-liberal establishment in this country.