The separation of powers within the federal government ensures that

Not all of the power rests in one persons hands.

The separation of powers within the federal government ensures that

no one branch can become too powerful. This separation is aided by

the system of checks and balances, examples of which include the

president's veto, the Supreme Court's rulings that a law is

unconstitutional, and Congress's power to impeach and even kick

the president, Supreme Court judges, and cabinet members.

Just a little extra info, just in case; )