Walker's opinion "reads as solid and careful work. I imagine it was written primarily for one pair of eyes - Justice Kennedy's," said Rick Hasen, a professor at Loyola Law School in Los Angeles.

Margaret Russell, a Santa Clara University law professor, said Walker's conclusion that Prop. 8 was based on moral disapproval of gays and lesbians was reminiscent of Kennedy's 1996 ruling in a Colorado case. Kennedy said a state law that barred local gay-rights ordinances was unconstitutionally based on disapproval of the people those ordinances protected.

Russell, who supports same-sex marriage, said the Supreme Court isn't likely to endorse Walker's conclusion that Prop. 8 violated a fundamental right to marry because the court hasn't previously recognized such rights for gay and lesbian couples. The justices could agree with Walker that the measure is unconstitutionally discriminatory, she said, but they might also draw different legal conclusions from the evidence he cited.

The ruling contained a withering critique of the case presented by Prop. 8's sponsors, who opposed holding a trial and argued that evidence of the initiative's intent and effects was legally irrelevant.