Fortunately, "We the People" have a contract that created the federal government and strictly limits the power of the President. This contract is the US Constitution. Unfortunately, very little is taught about this contract in public schools and if "We the People" don't enforce the provisions of the contract, then a President could very well become a dictator.
President Obama (who is a lawyer by profession) has said that he considers the Constitution to be a living document. That is like the builder you contracted with to build your house, saying that your contract should be interpreted according to current events, e.g. the economy drops so now he is going to leave off the 2 car garage you wanted and charge you the same amount.