Why do most Americans belive that the President is King?

I ask this because people keep acting like one man can change all the laws of the country, that if edwards were elected he could tell congress what to do, or if Obama is elected he'll make all these changes, or how Ron Paul would end all public funded programs... and people believe that one man elected can do this. I thought America was a represenative democracy, with three branches, not one. So why does everyone pretend that the President can change everything, why does he get all of the balme or all of the credit? This is America not a monarchy... So why do we act like we are voting for our king?