Court watchers speculate that some of the conservative members of the court who are uncomfortable with a lower court decision that struck down a successful ballot initiative, might have a greater concern with Justice Anthony Kennedy's ultimate vote. While it only takes 4 justices to agree to take a case, it takes 5 to win and Kennedy is seen as a likely swing vote.
"Conservative justices hoping to find an ally in Justice Kennedy may be concerned about his majority opinion in favor of gay rights advocates in two previous cases in 1996 and 2003," professor Margaret Russell of the Santa Clara University School of Law said.
"Kennedy's basic approach in those cases was to protect the individual liberty and choices of gay men and lesbians."
Other justices might vote against taking up the case out of a belief that the issue should be allowed to percolate further at the state level.
Indeed, many gay rights advocates have been working for years to focus their attention to get a consensus at the state level on the issue of gay marriage, rather than go prematurely to the Supreme Court and get a ruling that could galvanize gay marriage foes or, alternatively, shut down legal avenues.
Nine states and the District of Columbia allow (or will soon allow) gay marriage.
Besides the Prop 8 case, called Hollingsworth v. Perry, the Justices Friday will also address several challenges to a federal law, the Defense of Marriage Act (DOMA) that defines marriage as between a man and a woman.
Such cases do not involve a fundamental right to gay marriage, as the couples involved are already legally married in their state. Instead, at issue is whether legally married same-sex couples (in states that allow gay marriage) can be denied federal benefits, such as Social Security survivor benefits and federal health care, that are available to opposite-sex couples.
The Obama administration decided in 2011 to no longer defend DOMA in court, arguing that it was unconstitutional. Two federal appeals courts have struck down the law.
In court briefs filed with the Supreme Court, Solicitor General Donald B. Verrilli Jr. writes about the impact of the law: "Although Section 3 of DOMA does not purport to invalidate same-sex marriages in those States that permit them, it excludes such marriage from recognition for purposes of more than 1,000 federal statutes and programs whose administration turns in part on individuals' marital status."
Because the government refuses to defend the law in court, Republican Speaker John Boehner of Ohio moved to intervene and appointed the U.S. House of Representatives Bipartisan Legal Advisory Group (BLAG) to do so.
Paul D. Clement serves as BLAG's lawyer and stresses that DOMA was enacted with strong majorities in both houses of Congress and was signed into law in 1996 by President Bill Clinton. In court briefs, Clement writes that DOMA was not meant to invalidate any marriages, but "simply asserts the federal government's right as separate sovereign to provide its own definition which governs only federal programs and funding."
Kenji Yoshino, a professor at New York University School of Law, believes that the court is more likely to take up one of the DOMA cases than the Prop 8 case. "I think the court is almost certain to take the DOMA cases, as they involve lower courts striking down a federal statute rather than a state law, as is the case in the Prop 8 case," he says.
"The DOMA case also asks the court for less, in that it does not affect the marriage law in any state. Rather it returns the Congress to its traditional posture of deferring to state definitions of marriage."