Why has the power of the presidency been cause for debate?

Ever since America won it's independence from Britain, this has been a debate because the people are afraid of creating another tyranny like King George. The three branches of the government are supposed to balance each other out, and no one should have more power than the other, so the debate over the president is very prominent. The country should not be ruled by one person, so the president should not be dictator and should not have too much power.