Cohens lived in DC, which had
a lottery. He tried to sell tickets in Virginia and got arrested, since
lotteries were illegal in Virginia.
At Trial, Cohens argued that
the Federal government had found that selling lottery tickets was not
illegal, and they trumped Virginia State law.
Since DC was ruled by
Congress, the DC lottery had the weight of Federal Law.
Virginia convicted Cohens. He
appealed to the US Supreme Court.
The Supreme Court upheld the
conviction.
The US Supreme Court found
that the DC lottery was not authorized in Virginia, so Cohens could still
be convicted for violating Viriginia law.
Virginia had argued that,
under the 11th Amendment their
decisions were unreviewable. Supreme Court disagreed, and basically
affirmed the decision in Martin v. Hunter's Lessee (14 U.S. (1 Wheat.) 304 (1816)), which held
that the US Supreme Court does have the authority to overturn the
decisions of State Courts.