For most of America's history, presidents were figureheads. Congress ran what there was of the federal government, and that didn't amount to much until the Great Depression and World War II, when presidents, starting with Franklin D. Roosevelt, vastly expanded the government. The postwar era also thrust America into a global leadership position, putting more burden--and more visibility--on presidents. More recently, TV puts everything the president says and does in front of everyone, 24x7. Polarization is a natural consequence of vastly expanded role presidents play and the visibility they have.

FDR, elected four times and widely regarded by historians as one of the three greatest presidents, was far and away the most polarizing of the 20th Century chief executives. So, too, is Obama, who is the worst president of the postwar era.