checks and balances
The checks and balances system was set up to make sure that one branch of government didn't get too powerful.
In this system the 3 branches of Government can each restrain each other in different ways.
For example, the president can veto a bill from congress and refuse to sign it. Also if congress has 2/3 of the vote it can override a veto. and the Supreme court can declare a law unconstitutional.