All nine justices have had a significant voice in both oral argument and Wednesday's rulings, but it may be one member of the court whose views may count most in the high-stakes quest for five votes -- a plurality ensuring victory.
Justice Anthony Kennedy authored the landmark 1996 Romer v. Evans decision, striking down a Colorado constitutional amendment that forbid local communities from passing laws banning discrimination against gays.
The moderate-conservative wrote for the 6-3 court majority, rejecting the state's argument the law only blocked gay people from receiving preferential treatment or "special rights."
"To the contrary, the amendment imposes a special disability upon those persons alone," said the 76-year-old Kennedy. "Homosexuals are forbidden the safeguards that others enjoy or may seek without constraint."
In dissent, Justice Antonin Scalia criticized the court for placing what he said was "the prestige of this institution behind the proposition that opposition to homosexuality is as reprehensible as racial or religious bias."
In 2003, Kennedy authored the court's decision overturning state laws criminalizing homosexual sodomy. At the time though, he cautioned the court was not endorsing the idea of same-sex marriage, saying the private conduct case at hand "does not involve whether the government must give formal recognition to any relationship that homosexual persons seek to enter."
That caution was further articulated in a March speech by Kennedy, when he said some issues are best left to the other branches. "I think it's a serious problem. A democracy should not be dependent for its major decisions on what nine unelected people from a narrow legal background have to say," he said.
By patiently letting legislatures and the voters decide the social and practical implications of same-sex marriage over the past decade, the high court is now poised to perhaps offer the final word on tricky constitutional questions. Or not.
The split 5-4 conservative-liberal bench has the option of ruling broadly or narrowly -- perhaps taking a series of incremental cases over a period of years, building political momentum and public confidence in the process.
The Prop 8 case is Hollingsworth v. Perry (12-144). The DOMA case is U.S. v. Windsor (12-307).