US Elections - How do they work?

Separation of Powers

The Government of the United States, the federal government, is divided into three branches:  the executive power, invested in the President, the legislative power, given to Congress (the House of Representatives and the Senate), and the judicial power, vested in one Supreme Court and other federal courts created by Congress.  The Constitution provides a system of checks and balances designed to avoid the tyranny of any one branch.

Most important actions require the participation of more than once branch of government.  For example, Congress passes laws, but the President can veto them.  The executive branch prosecutes persons for criminal violations, but they must be tried by the courts.  The President appoints federal judges, but their appointment must be confirmed by the Senate.