Separation of Powers
The three branches, Legislative, Executive and Judicial, have what is called the principle of separation of powers. This means that each branch of government must rely on the other for approval, so that no one power can make decisions without the other.
Just to illustrate this tit-for-tat concept, the Legislative branch makes laws, the Executive branch enforces those laws and the Judicial branch interprets those laws. If Congress writes a law, the Supreme Court can declare it unconstitutional. Congress can also rewrite legislation to circumvent the Court’s decisions and the Senate confirms the judges and determines the number of judges appointed.
In other words, they all have a way to oversee, alter and compromise the other chambers’ powers, so no one branch can be a bully. They may use the “bully pulpit" (a conspicuous place to speak out) in order to make a point, but they cannot force an unpopular idea without the aid and compromise of the others.
The President of the United States has powers such as the ability to can nominate federal judges, refuse to enforce the Court’s decisions and grant pardons. Congress can override a presidential veto of its legislation or remove and impeach a president and the Senate confirms presidential appointments. the Supreme Court can declare presidential actions unconstitutional. That is separation of powers!