U.S. District Court Judge Vaughn R. Walker, ruling after a nearly two-hour hearing in San Francisco, rejected arguments by Proposition 8's proponents that precedent and tradition showed last November's ballot measure to be permissible under the U.S. Constitution. Walker's decision means the case will proceed to trial as scheduled in January, unless appeals delay it. The California Supreme Court ruled in May that Proposition 8, approved by 52.3 percent of voters, did not violate the California Constitution. The lawsuit before Walker makes the case that the measure violates the U.S. Constitution's guarantees of equal protection and due process. During Wednesday's hearing, Charles Cooper, representing the Proposition 8 campaign, argued that marriage historically has been reserved for unions between a man and a woman because only opposite-sex couples can procreate 'naturally.' Walker, however, noted that not all married couples can procreate. 'Just last month,' Walker said, 'I performed a wedding in which the groom was 95 and the bride was 83. I did not demand that they prove they would engage in procreation.' Proposition 8 backers also argued that precedent required Walker to uphold the measure as constitutional. They cited a 1972 case involving a Minnesota law that limited marriage to unions between a man and a woman. The Minnesota Supreme Court rejected an equal-protection challenge, and the U.S. Supreme Court declined to hear an appeal. 'We can't put much stock in that case, can we?' Walker told the lawyers. He described the case as 'old,' 'very limited' and 'not a considered decision of the (U.S.) Supreme Court.' In his ruling, Walker noted that Proposition 8 stripped gays and lesbians of the right to marry, which they had been given six months earlier in a historic 4-3 ruling by the California Supreme Court. 'Potentially, Proposition 8 may be invalid given the history in California, while similar actions in another state ... may not be constitutionally infirm,' Walker said. Walker also rejected the campaign's contention that Proposition 8 must be upheld if justified by 'rational' reasons. Walker said the U.S. Supreme Court had not made clear the legal standard for weighing claims of discrimination on the basis of sexual orientation. Walker previously ordered the Proposition 8 campaign to disclose its internal strategy memorandums and communications, an order the campaign is appealing to the 9th U.S. Circuit Court of Appeals on First Amendment grounds. Theodore Olson, representing same-sex couples in the case, told Walker that if the appeal delayed the trial, he might ask for a preliminary injunction to suspend Proposition 8. 'If the case should hang up on a discovery issue,' Walker acknowledged, 'that does change the equation.' A ruling on a preliminary injunction could be appealed, and higher courts could resolve Proposition 8's constitutionality without a trial. Walker said he thought it would be 'unfortunate to short-circuit the process' that way. Walker ordered written arguments on a request by the Proposition 8 campaign to remove Attorney General Jerry Brown as a defendant and make him a plaintiff in the case. Brown, who was sued in his position as the state's chief law-enforcement officer, has said in court papers that he agrees with plaintiffs that the ballot measure was unconstitutional. Brown and the plaintiffs oppose the realignment. 