A Bill of Attainder is defined by Wikipedia as: “an act of the legislature declaring a person or group of persons guilty of some crime and punishing them without benefit of a trial...”

Specifically prohibited under Article I, Section 9, Clause 3 of the U.S. Constitution, the Framers succinctly state:

 “No bill of attainder or ex post facto Law shall be passed.”

The father of the U.S. Constitution, James Madison, wrote in 1788:

“Bills of attainder, ex post facto laws, and laws impairing the obligations of contracts, are contrary to the first principles of the social compact, and to every principle of sound legislation. ...  Very properly, therefore, have the convention added this constitutional bulwark in favor of personal security and private rights. … The sober people of America are weary of the fluctuating policy which has directed the public councils. They have seen with regret and indignation that sudden changes and legislative interferences, in cases affecting personal rights, become jobs in the hands of enterprising and influential speculators, and snares to the more-industrious and less-informed part of the community.”