In the much anticipated opinion in Perry v. Schwarzenegger, Chief Judge of the U.S. District Court for the Northern District of California, Vaughn Walker, found on August 4 that California's law banning same sex marriage violates the Constitution of the United States. Proposition 8 was passed by a narrow margin of voters in 2008. Previous to its passage, 18,000 same sex couples were granted marriage licenses in the state of California. Today's Prop 8 ruling, like those before from the state courts, does not affect those marriages.
In his opinion, Judge Walker found the state law violated both the Equal Protection and the Due Process clauses of the Constitution. SCOTUS Blog writes that after consideration, the court found that the proponents of Prop 8 did not show that the state had a rational basis (the lowest of the tests for constitutional validity applied by the courts) for excluding same sex couples from the right to marry. The judge found the law specifically, "... fails to advance any rational basis in singling out gay men and lesbians for denial of a marriage age license. Indeed, the evidence shows Proposition 8 does nothing more than enshrine in the California Constitution the notion that opposite sex couples are superior to same-sex couples ..."