(ABC NEWS) -- Supreme Court justices seemed to struggle with the notion of extending marriage rights to same-sex couples as they grilled lawyers Tuesday morning in a potentially landmark case over California's ban on gay marriages.
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As the politics change by the day, the court heard a case -- Proposition 8 -- that could drastically change how states and the federal government approach one of the touchiest social issues of the past decade.
The justices challenged lawyers on both sides on common points of contention that arise whenever gay marriage is debated.
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All eyes were on Justice Anthony Kennedy, whose vote could be essential in the case.
At one point he talked about the children of gay couples, noting that they wanted their parents' unions to be recognized. "The voice of these children is important," Kennedy said.
But later he told the lawyer for gay couples challenging the ban that the issue was in "unchartered waters."
Kennedy also questioned whether the court should be considering Prop 8 and whether the California couple challenging it had the legal "standing" to bring their case -- raising the possibility that the Supreme Court could punt on the merits of Prop 8, declining to set a federal precedent on gay marriage in this case and deferring to a lower court's ruling to overturn California's ban.
Justice Elena Kagan, President Obama's second appointee to the court, asked the lawyer defending California's gay marriage ban what harm would be done to heterosexual marriage if gay and lesbian marriages were legally recognized. He answered that same-sex marriage would do harm that is difficult now to foresee.
Justice Antonin Scalia, widely recognized as one of the court's more conservative justices, engaged in intense debate with pro-gay-marriage lawyer Ted Olson.
"When did it become unconstitutional to exclude homosexuals from marriage?" Scalia asked.
Some justices questioned the main argument against gay marriage, that the government has a societal interest in traditional marriage for "responsible procreation."
Kagan asked about marriage licenses issued to heterosexual couples who are older than 55. "Not a lot of children" come out of such marriages, she said.
Justice Ruth Bader Ginsburg asked about heterosexual couples locked up in prison. "No possibility of procreation there," she pointed out.
Along with another case scheduled for Wednesday, in which the court will consider a challenge to the federal Defense of Marriage Act (DOMA) ban on gay marriage, the Prop 8 case likely will lead to at least one landmark decision to be cited by advocates and opponents of same-sex marriage for decades to come.
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On behalf of a California couple, Prop 8 is being challenge by the unlikely bipartisan duo of Olson and David Boies, who argued before the court on opposite sides of the 2000 case over Florida's vote recount in the presidential election between George W. Bush and Al Gore. Boies served as the top lawyer for Gore's campaign; Olson, for Bush's.
The pair was brought together by gay-rights advocates seeking to overturn California's ban, which took the gay activist community by surprise when it passed in 2008. Californians voted 52 percent to 48 percent in favor of banning gay marriage under their state constitution in 2008 on the same day they voted Barack Obama into the White House by a margin of 61 percent to 37 percent for Sen. John McCain, R-Ariz.
Charles J. Cooper, representing a group called Protectmarriage.com, argued in favor of the ban.
Supporters of Prop 8 have contended that states should be able to ban gay marriage because society has an interest in heterosexual marriage as a means of procreation.
"The definition of marriage has always been understood to be the virtually exclusive province of the states, which, subject only to clear constitutional constraints, have absolute right to prescribe the conditions upon which the marriage relation between their citizens shall be created," Cooper has said.
Boies and Olson, meanwhile, contend that Prop 8 singles out gay couples unfairly.
"The unmistakable purpose and effect of Proposition 8," they have written, "is to stigmatize gay men and lesbians -- and them alone -- and enshrine in California's Constitution that they are unequal to everyone else, that their committed relationships are ineligible for the designation 'marriage' and that they are unworthy of that most important relation in life."
Tuesday morning, activists on both sides had gathered outside the court.
Sporting gloves and puffy jackets, pro-gay-marriage activists displayed signs saying, "Marriage is a human right not a heterosexual privilege" and "the nation is ready for marriage equality."
Joey Williamson had been outside the court for 49 hours and had at least another 24 to go, having traveled from New York City waiting to hear the arguments against the Defense of Marriage Act tomorrow.
"Obviously these are hugely historic cases," Williamson says. He saw the state Supreme Court case back home in New York so tomorrow will wrap off a long saga for him. "We thought if we could see this case all the way to the end it would be super interesting."
Michael Krzywols traveled from Rhode Island with the Faith Alliance to Preserve the Sanctity of Marriage because he thinks it's important to stand up for the values he grew up with. He said marriage is an issue that has folks riled up in his state.
"A lot of people that were for a man and a woman are changing their positions all l of a sudden and just as of yesterday a lot of the mayors are getting involved," Krzywols told ABC Tuesday.
The National Organization for Marriage organized a march outside the Supreme Court that evened out the crowd, as gay-marriage supporters had outnumbered opponents earlier Tuesday morning.
The arguments on Prop 8 came after a week and a half of snowballing support for gay marriage by public figures.
Earlier this month, Ohio Republican Sen. Rob Portman became only the second sitting GOP senator ever to endorse gay marriage, citing his gay son as a reason for his changed opinion.
Former Secretary of State Hillary Clinton endorsed gay marriage last week. This week, Democratic Sens. Claire McCaskill, Mo., and Mark Warner, Va., publicly acknowledged their support for allowing gay couples to marry.
Obama later endorsed gay marriage in a 2012 interview with ABC News' Robin Roberts.
The Prop 8 and DOMA cases come before the court as popular opinion has swung in favor of allowing gay marriage.
A recent ABC News/Washington Post poll showed massive gains for gay marriage in the last decade. In the March 7-10 survey, 58 percent of respondents said they think gay marriage should be legal, while 36 percent opposed it - a near inversion of the widespread opposition to gay marriage shown in ABC/Post polling from 2003.
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