In Whelan v. The United States, the Supreme Court considered a case involving an alleged violation of the Fourth Amendment's prohibition against unreasonable searches and seizures. At issue was whether or not a search warrant issued by a federal court in Pennsylvania could be used to search for evidence in Maryland without violating the Constitution. The Supreme Court held that it could not, ruling that such warrants must be limited to searches within their own jurisdiction unless Congress has specifically authorized otherwise. This decision established an important precedent regarding how far federal courts can extend their authority when issuing search warrants and helped ensure that citizens' rights under the Fourth Amendment are respected across state lines.

Justice Johnson delivered the dissenting opinion in Whelan v. United States, arguing that Congress had exceeded its authority by passing a law to punish an act of treason committed before the passage of said law. He argued that such a punishment was unconstitutional because it violated Article I Section 9 Clause 3 of the Constitution which states "No Bill of Attainder or ex post facto Law shall be passed." Justice Johnson further argued that since no one can be punished for an act not deemed illegal at the time it was committed, this case should have been dismissed and Whelan acquitted on all charges. In conclusion, he stated that if Congress could pass laws punishing acts done prior to their enactment then there would be no limit to their power and they could make any action criminal regardless when it occurred.