WASHINGTON -- It's not often that people camp out for days waiting on a courtroom seat.
Then again, it's not often that a court case offers the blend of emotional drama, legal significance and widespread social impact promised by Tuesday's U.S. Supreme Court arguments on same-sex marriage.
At stake: nothing less than how America defines marriage.
People who have camped outside the Supreme Court building in frigid temperatures and snow -- some since Thursday -- will file inside Tuesday morning to watch attorneys argue for and against California's Proposition 8.
The voter-approved ballot initiative banned same-sex marriage in California.
Activists on both sides of the issue will stay outside to stage competing rallies.
On Wednesday, justices will hear arguments in a separate case involving the federal Defense of Marriage Act, which, like the California law, defines marriage as between a man and a woman.
The law bars the federal government from recognizing state-sanctioned same-sex marriages. It prevents legally married gay and lesbian couples from getting federal benefits and privileges, like tax breaks and survivor benefits, that are extended to opposite-sex married couples.
What the court decides could mark a historic shift in how the law treats marriage, striking down laws across the country banning same-sex marriage and matching an apparent cultural shift toward acceptance of same-sex couples.
Or the court could leave the current patchwork of state laws in place, choosing to let state legislatures and courts sort it all out.
Forty-one states now forbid same-sex marriage, although nine of them do allow civil partnerships. Nine other states allow same-sex marriage, and about 120,000 same-sex couples have gotten married, according to estimates.
The state bans seem to run counter to polls that show rising support overall for same-sex marriage. A CNN/ORC International poll released Monday found that 53% of Americans now support same-sex marriage, up from 40% in 2007.
No immediate decision
The court is unlikely to announce its decision until June.
But we could get a sense of which way the decision will go by listening to the questions posed by Justice Anthony Kennedy, said CNN senior legal analyst Jeffrey Toobin.
The court's four liberal justices are likely to vote to overrule Proposition 8, he said. Four conservatives are likely to vote to keep it.
"The most likely person to give the fifth vote is Anthony Kennedy," who previously authored two important gay rights decisions, Toobin said.
Partisans speak out
Same-sex marriage supporters say it's time for the court to take a stand that puts all Americans on the same footing.
"This is about our equality," said Paul Katami, one of the plaintiffs in the California case. "This is about our freedom and our liberty. So we are not trying to topple marriage. We are not trying to redefine marriage. What we are trying to say is that equality is the backbone of our country."
But supporters of Proposition 8 and DOMA say the Supreme Court should stay out of the issue and let voters decide what they want.
"Our most fundamental right in this country is the right to vote and the right to participate in the political process," said Austin Nimocks of the Alliance Defending Freedom, a Christian advocacy group.
"We don't need the Supreme Court to take that right away from Americans of good faith on both sides of this issue and impose its judicial solution," Nimocks said. "We need to leave this debate to the democratic process, which is working."
Tuesday's action inside the court's ornate marble courtroom concerns the appeal of a federal judge's decision striking down California's Proposition 8.
The measure defines marriage as between a man and a woman. Voters approved the proposal 52% to 48% in November 2008, less than six months after the state Supreme Court ruled that marriage was a fundamental right that must be extended to same-sex couples.
The overriding legal question is whether the 14th Amendment guarantee of equal protection under the law prevents states from defining marriage as California has.
Two of the key plaintiffs are Katami and Jeff Zarrillo, a Burbank, California, couple who want to marry but can't because of Proposition 8. They say the state is discriminating against them for their sexuality.
"Stigma is stigma. And discrimination is discrimination," Katami told CNN. "I think that any time there's discrimination in the country, it needs to be addressed and it needs to be taken care of. And that's why we feel that anytime in our history when there's been racial discrimination or sexual discrimination of orientation, or in particular marriage at this point, that we always bend toward the arch of equality."
In its ruling, the Supreme Court could establish or reject a constitutional right to same-sex marriage or limit its decision to California's law alone.
General Kamala Harris, who is arguing against Proposition 8, said voter-approved marriage bans "are simply unconstitutional."
The Supreme Court has ruled more than a dozen times that marriage is a fundamental right, "and as it relates to a fundamental right, the court will hold that under the highest level of scrutiny," Harris said.
The Obama administration has formally expressed support for same-sex marriage in California, weighing in on the case in a brief last month. Obama, whose views on the issue have evolved over his political career to full support, said that he would vote to strike down the state's law if he sat on the court.
In what some have labeled the "nine-state strategy," the Justice Department argument is expected to center on the idea that civil union and domestic partnership laws may themselves be unconstitutional and that those states should go all the way and grant same-sex couples full marriage rights.
Other prominent politicians have expressed timely opinions in recent weeks, indicating the importance of the matter in the social context of 21st century American politics.
Hillary Clinton, the former secretary of state and possible 2016 Democratic presidential candidate, recorded a video for a gay rights group indicating her support.
Republicans have described cracks appearing in their party's long-held opposition to same-sex marriage.
"There is no putting this genie back in the bottle. It is undeniable. The shift is here and we're not going back." Republican strategist and CNN contributor Ana Navarro said Sunday.
One prominent Republican, Sen. Rob Portman of Ohio, endorsed it this month after his son revealed to him that he was gay.
The case being heard Tuesday is Hollingsworth v. Perry (12-144), dealing with Proposition 8. And coming up Wednesday is U.S. v. Windsor (12-307), which deals with the DOMA issue.
Bill Mears reported and wrote from Washington, Michael Pearson reported and wrote from Atlanta; CNN's Joe Johns, Alan Duke and Samira Jafari contributed to this report.