May 15th, 1939: the Supreme Court issued its decision in United States v. Miller, upholding a blatantly unconstitutional Roosevelt tax collection measure. The decision was as terse as it was incoherent, both factors being due to the fact that it was hastily authored by a lazy Justice behind on his quota.
The resulting decision would cement the idea that the 2nd Amendment was somehow a "collective" right, tied only to service in a state-run militia, and sometimes not even then. Furthermore, it would serve as ammunition in countless briefs and cases affirming restrictions on the 2nd Amendment.