The US Supreme Court on Tuesday takes up the emotionally charged issue of gay marriage as it considers arguments that it should make history and extend equal rights to same-sex couples.
A pro-gay marriage protester stands in front of the US Supreme Court on March 26, 2013 in Washington, DC.
Waving US and rainbow flags, hundreds of gay marriage supporters braved the cold to rally outside the court along with a smaller group of opponents, some pushing strollers. Some slept outside in hopes of witnessing the historic hearing.
The actor and activist Rob Reiner, who held a red admission ticket, said he was unsure how the nine-justice Supreme Court would rule but that he was confident gay marriage would eventually be available for all Americans.
"It's the last big piece of the civil rights puzzle hopefully falling into place," Reiner said. "We feel like this is not a matter of if, but of when."
Over two days, the Supreme Court will listen to lawyers from both sides on gay marriage, which is allowed in nine states and the District of Columbia but which activists hope will become a nationwide right. A decision is not expected for several months.
The top court will first hear arguments over the constitutionality of Proposition 8, in which California voters in 2008 ended the right to same-sex marriage in the nation's most populous state.
The two couples who are plaintiffs staged a photo opportunity on Monday by inspecting the original handwritten text of the US Constitution on the eve of their day in court.
Paul Katami and Jeff Zarrillo joined Kris Perry and Sandy Tier on the steps of the National Archives in the US capital, where they posed for photographers but declined to speak to reporters.
They then went in "to view the US Constitution and reflect on the importance of their case for gay and lesbian couples across the nation," said the American Foundation for Equal Rights, which supports their case.
Then on Wednesday, the court will consider the Defense of Marriage Act, a federal law which defines marriage as an act between a man and woman and thus denies married gays and lesbians the same rights and privileges.
The star plaintiff in that case is Edie Windsor, 83, who had to pay $363,000 in federal estate taxes when her partner of more than 40 years, Thea Spyer, whom she had married in Canada in 2007, died in 2009.
Under the law, the surviving member of a heterosexual married couple is exempt from such taxes.
Outside the Supreme Court, color-coded protesters -- red for supporters of gay marriage and red, white and blue for opponents -- set out their positions in the court of public opinion.
One demonstrator dressed in pink and danced to music of Lady Gaga, the superstar singer and supporter of gay rights. Among opponents, protesters chanted, "Every child deserves a mom and dad."
Opinion polls have repeatedly indicated that most Americans accept the principle of same-sex marriage, including an overwhelming majority of younger Americans.
President Barack Obama -- who last May became the first US president to publicly say he was in favor of gay marriage -- restated his support for it on Monday through a Twitter account managed in his name by Organizing for Action, an advocacy group founded after his re-election.
"Every American should be able to marry the person they love," read the tweet, which carried the hashtag "#LoveIsLove."
Former president Bill Clinton has taken the unusual step of encouraging the Supreme Court to strike down the Defense of Marriage Act, even though he signed it into law in 1996.
But opposition -- spearheaded by social conservatives and backed by the Roman Catholic and evangelical churches -- remains strong, with many contending that marriage can only be a union between a man and a woman.
"We believe it is imperative that political leaders, the media and the culture see that we care about protecting marriage enough to stand up and march for it," said a message by the National Organization for Marriage, which is organizing a rally against same-sex marriage.
Vigils for marriage equality were taking place throughout the United States, and the Los Angeles Times reported that a lesbian cousin of Chief Justice John Roberts would be in court on Tuesday.
Roberts, nominated to the court by former president George W. Bush, is generally considered a conservative but he played a key role in the Supreme Court's decision to uphold Obama's controversial health care reform package.
Another critical member of the bench is Anthony Kennedy. A conservative, he has upheld gay rights in the Supreme Court, but also warned against democracies depending on their judiciaries to sort out their political rows.