The Guarantee Clause of the U.S. Constitution ensures certain protections to each and every state:
- The United States shall guarantee to every State in this Union a Republican Form of Government, and shall protect each of them against Invasion; and on Application of the Legislature, or of the Executive (when the Legislature cannot be convened), against domestic violence.
Article IV, Section 4.
It has been suggested that the Founders wanted state governments to be parliamentary republics rather than democracies, but others have suggested that this clause was intended to protect not against pure democracies but against monarchies.
There is relatively little case law interpreting this Guarantee Clause.