Obviously, there are many more players in the game of politics in a democracy.
Constitutionally, the Supreme Court has unique powers, and the latent power to nullify acts of Congress and the President.
The federal bureaucracy and the media are two enormous players in politics. Then, there is the interaction between academics, think tanks, politicians and the political process. Media, bureaucrats, and academia have a substantial influence, which is a quantum power over the individual citizen.