The President is head of Government, He is the most powerful individual in the whole government, Other branches are powerful but not individually but as a collective. Like the Legislative which comprises of the Senate and House of Representative, Together they can impeach the President. Which shows strength in numbers.
If you take the American form of government, then the last word is still for the president, although the Senate also has levers of influence on the president's decision. In the right constitutional state, all branches of power must be balanced in order to avoid dictatorship.