That appeals court ruling applied only to California, where same-sex couples briefly had the right to marry before the state's voters in November 2008 adopted Proposition 8, a constitutional amendment that defined marriage as the union of a man and a woman.
Several members of the court also were troubled by the Obama administration's main contention that when states offer same-sex couples civil union rights of marriage, as California and eight other states do, they also must allow marriage. The other states are: Colorado, Delaware, Hawaii, Illinois, Nevada, New Jersey, Oregon and Rhode Island.
"So a state that has made considerable progress has to go all the way, but at least the government's position is, if the state has done absolutely nothing at all, then it can do as it will," Justice Ruth Bader Ginsburg said.
Chief Justice John Roberts questioned whether gay marriage proponents were arguing over a mere label. "Same-sex couples have every other right. It's just about the label," Roberts said.
In the California case, if the court wants to find an exit without making a decision about gay marriage, it has two basic options.
It could rule that the opponents have no right, or legal standing, to defend Proposition 8 in court. Such an outcome also would leave in place the trial court decision in favor of the two same-sex couples who sued for the right to marry. On a practical level, California officials probably would order county clerks across the state to begin issuing marriage licenses to gay and lesbian couples, although some more conservative counties might object.
Alternatively, the justices could determine that they should not have agreed to hear the case in the first place, as happens a couple of times a term on average. In that situation, the court issues a one-sentence order dismissing the case "as improvidently granted." The effect of that would be to leave in place the appeals court ruling, which in the case of Proposition 8, applies only to California. The appeals court also voted to strike down the ban, but on somewhat different grounds than the trial court.
Reflecting the high interest in this week's cases, the court released an audio recording of Tuesday's argument shortly after it concluded and plans to the do same Wednesday. Tuesday's audio can be found at: http://tinyurl.com/dxefy2a. The last time the court provided same-day audio recordings was during its consideration of Obama's health care law.
Both sides of marriage question were well represented outside the courthouse. Supporters of gay marriage came with homemade signs including ones that read "a more perfect union" and "love is love."
Among the opponents was retired metal worker Mike Krzywonos, 57, of Pawtucket, R.I. He wore a button that read "marriage 1 man + 1 woman" and said his group represents the "silent majority."
Same-sex marriage is legal in nine states and the District of Columbia. The states are Connecticut, Iowa, Maine, Maryland, Massachusetts, New Hampshire, New York, Vermont and Washington.
Thirty states ban same-sex marriage in their constitutions, while ten states bar them under state laws. New Mexico law is silent on the issue.
Polls have shown increasing support in the country for gay marriage. According to a Pew Research Center poll conducted in mid-March, 49 percent of Americans now favor allowing gays and lesbians to marry legally, with 44 percent opposed.
A good part of the give-and-take Tuesday concerned Cooper's argument that the state has a legitimate interest in limiting marriage to heterosexuals since they have the unique ability to have children.
He and Justice Elena Kagan engaged in a lengthy, sometimes humorous, exchange on the topic.
If a state can use the ability to have children as a reason to prohibit same-sex marriage, what about couples over the age of 55? Kagan asked.
"Your Honor, even with respect to couples over the age of 55, it is very rare that both parties to the couple are infertile," Cooper said.
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