Gay Marriage, Round 2: Supreme Court Weighs DOMA March 27, 2013 - Since 1996, the federal government has defined marriage as between a man and a woman. That could change if proponents of gay marriage succeed before the Supreme Court. For the second straight day, the nation's highest court will hear arguments in a high-profile case on gay marriage, one of the hottest social issues in America. Read More About Gay Marriage from ABC News On Tuesday, the justices heard a challenge to California's Proposition 8 ban on gay marriage. Today, they will hear arguments in a challenge to the Defense of Marriage Act, the 1996 law signed by President Bill Clinton that defined marriage as heterosexual and denied federal benefits to gay couples, who are legally married in their state. Between the two cases, the Supreme Court could issue a landmark ruling on gay marriage by the end of June. Read more: Supreme Court Justices Struggle With Federal Right to Gay Marriage The DOMA challenge was brought by Edie Windsor, an 83-year-old woman from New York who married Thea Clara Spyer in 2007. After Spyer's death in 2009, Windsor was denied an exemption of federal estate taxes. DOMA has enraged gay-rights activists, some of whom have harbored resentment at Clinton for signing it into law in the first place. Almost as soon as President Obama took office, activists urged the administration to oppose DOMA. In February 2011, they got their wish, as Attorney General Eric Holder announced in a letter to Congress that the Department of Justice would no longer defend DOMA in federal court. The Obama administration has argued that DOMA should be overturned, while House Republicans have stepped in to defend it, tasking the Bipartisan Legal Advisory Group (BLAG) with arguing for DOMA in federal court. Today, BLAG's top lawyer, George W. Bush's former solicitor general, Paul Clement, will argue before the justices that DOMA should be upheld. In his briefs, Clement has argued that the federal government does not invalidate any state laws allowing gay marriage, but instead ensures that federal benefits are distributed uniformly throughout the states. Current Solicitor General Donald B. Verrilli, who appeared before the court on Tuesday to weigh in against California's marriage ban, has argued that DOMA unfairly denies federal benefits to gay married couples. "The law denies tens of thousands of same-sex couples who are legally married under state law an array of important federal benefits that are available to legally married opposite-sex couples," Verrilli has written. Before considering the merits of DOMA, the court will have to consider two threshold issues: whether it even has jurisdiction to hear the case given that the Obama administration believes DOMA should be overturned, and whether BLAG has legal "standing" to defend it. Both sides want the court to consider the merits of DOMA, so the court has appointed Harvard law professor Vicki Jackson to argue the threshold issues. On Tuesday, supporters and opponents of gay marriage gathered outside the Supreme Court to hold signs and make their voices heard. The justices struggled with the notion of extending marriage rights to gay couples, pressing lawyers on both sides of the Prop 8 case. All eyes will once again focus on Justice Anthony Kennedy, viewed as the court's key swing vote on gay marriage. On Tuesday, he asked some conflicting questions on the issue of the lawyers arguing before him. "The voice of these children is important," Kennedy said at one point, noting that children of gay couples want their parents' unions to be recognized as marriages. However, later he told the lawyer for gay couples challenging the ban that the issue was in "uncharted waters." The court is considering these two potentially landmark gay-marriage cases as the politics of the issue shift by the day. After Ohio Republican Sen. Rob Portman announced his support for gay marriage earlier this month, becoming the only current GOP senator to hold that position, a herd of Democratic senators have stampeded toward the marriage issue. Sens. Claire McCaskill, D-Mo., Mark Warner, D-Va., Jon Tester, D-Mont., and Mark Begich, D-Alaska, have all announced their support for gay marriage this week. Public opinion, too, has shifted drastically on gay marriage in the last decade. A recent ABC News/Washington Post poll, taken March 7-10, showed 58 percent of respondents in support of gay marriage, while 36 percent opposed it. That's nearly the opposite of public opinion on gay marriage in 2003, when ABC/Post polling showed 37 percent support and 55 percent opposition.