Laws are generally not retroactive (though admittedly this principle does get violated). > The Ex Post Facto Clause, contained in Article I, Section 9, Clause

Laws are generally not retroactive (though admittedly this principle does get violated). > The Ex Post Facto Clause, contained in Article I, Section 9, Clause 3 of the Constitution, provides: “No . . . ex post facto Law shall be passed.” The phrase “ex post facto,” Latin for “after the fact,” refers to laws that apply retroactively. While the Ex Post Facto Clause on its face might appear to bar all retroactive legislation, courts have applied the Clause only to penal laws. > Congress has much greater leeway to enact retroactive legislation in the civil sphere than in the criminal sphere. However, certain constitutional limits apply, and courts interpreting ambiguous statutes apply a general presumption against retroactivity. https://sgp.fas.org/crs/misc/IF11293.pdf https://sgp.fas.org/crs/misc/IF11293.pdf