Article Three of the United States Constitution
The last section of Article 3 talks about treason and how it should be punished.  The Founding Fathers wanted to make sure that Americans' rights were protected.  They also knew that in the past, in England, some kings had gotten rid of their political opponents just by accusing them of treason.  For these reasons, the Founders wanted to make sure the Constitution said specifically what crimes were treason; what would be needed to find people guilty; and what the punishments could be.