Checks and balances, yo! Let's see if I can still remember this from, like, fifth grade: executive (the President), legislative (Congress), and judicial (umm... I want to say Supreme Court? or are state courts included?). Legislative makes laws, judicial interprets laws and can declare them unconstitutional, and sadly I'm not that goddamn SURE what the President does, though I do know he can veto things and be figureheady. Ahem. [/jaded]