Understanding the form the U.S. government takes is crucial to understanding the impeachment process. The U.S. Constitution provides for three branches of government:
This separation of powers means that no one branch of government is more powerful than the other, and that there is a system of checks and balances by which any given branch may correct errors or oversteps committed by another branch. Presidential impeachment, for instance, is a means by which the legislative branch may check--that is, curb or rein in--the executive branch.
[Infographic courtesy of USA.gov. Click here for more information about the three branches of the United States government.]