This picture shows that the three branches, Executive, Judicial, and Legislative watch each other with the Checks & Balances system.
The Checks & Balances system makes sure that no one branch or entity is more powerful than the other for fear of tyranny. The founding fathers were inspired by Enlightenment Philosopher, Montesquieu, to separate the powers. Executive being in charge of enforcing the laws, Legislative's work is to create the laws for our country, and Judicial's job is to interpret the laws. All three branches are capable of limiting the other.