Five years, thousands of weddings, dozens of lawsuits, and one tense referendum after gay couples were first allowed to tie the knot in California, the state's Supreme Court is poised to once more decide their future.
A panel of seven judges will announce tomorrow whether Proposition Eight, a same-sex marriage ban approved by a narrow majority of voters in November, should now be tossed out because of claims that it was put to the ballot improperly. The court, which has been considering the matter since March, will also reveal the fate of 18,000 couples who married in a five-month period last year when same-sex weddings were allowed. They have been in legal limbo since.
Most experts expect existing marriages to be upheld, but say the court is unlikely to contravene the democratically expressed wish of a slim majority of Californians by overturning Proposition Eight, which was approved by 52 per cent of voters.
Whatever the verdict, a string of demonstrations is already scheduled tomorrow. If the ban is upheld, organisers of at least one event, at San Francisco's City Hall, say large numbers of attendees plan to be "arrested in civil disobedience".
Gay marriage rivals abortion and gun control among America's most divisive social issues, pitting well-funded lobby groups on the religious Right, who claim it undermines traditional family values, against equally trenchant proponents on the liberal Left.
The issue has prompted angry protests and widespread consumer boycotts. Last month, it even overshadowed the Miss USA pageant, when the runner-up, California's Carrie Prejean, was subjected to a vicious smear campaign after voicing opposition to same-sex unions.
Since Proposition Eight passed, four states – Iowa, Vermont, Maine and Connecticut – have legalised the practice, joining Massachusetts, where it has been legal for several years. Another such law is pending in New Hampshire.
But California, as America's most populous state, is seen as the nation's most important "bellwether". Despite the traditionally liberal leanings of Californians, the state is evenly balanced on the issue, thanks to its large Hispanic population which takes a Catholic view on social issues.
Awaiting the outcome of the challenge to Proposition Eight has been an "an absolutely gut-wrenching experience", Molly McKay, of Marriage Equality USA, told the Associated Press. "As Californians, we are all under tremendous strain worrying about the economy, our jobs and our families," she said. "Gay families have been living for months with the fear that the court will allow a bare majority of voters to strip gay and lesbian families of their constitutional protections."
This turbulent saga began in 2004, when the Mayor of San Francisco, Gavin Newsom, unilaterally decided to begin issuing marriage licences to gay couples in the city. Local courts soon intervened, ruling that Mr Newsom had overstepped his authority. But last May, the State Supreme Court upheld an appeal, deciding that California's constitution provides a "fundamental" right to marry that should extend to all couples, regardless of their orientation.
Thousands of couples were married between May and November last year but new weddings were halted after election day, when Proposition Eight narrowly passed after an $80m (£55m) battle that made it the most expensive ballot measure on a social issue in US history.
The appeal being decided tomorrow revolves around a legal technicality: supporters of gay marriage claim that Proposition Eight changed the state's constitution, and therefore should not have been put to the public vote until it had been approved by two-thirds of the state's lawmakers.
The State's attorney general, Jerry Brown, agreed in March that they have a case under Californian law. But most of those close to the issue do not expect the Supreme Court to look particularly favourably upon it. "The court is very, very reluctant to frustrate the will of the people as demonstrated by their vote," said Gerald Uelman, a law professor and expert on the State Supreme Court. "If they agree [the right to same-sex marriage] is so fundamental that to abolish it revises the constitution, they would have to admit they revised the constitution in the first place."
In the likely event that the court upholds the ban, proponents of gay marriage will try to have it overturned by democratic means, with a fresh ballot measure in either 2010 or 2012. Like voters across the rest of the country, a small majority of Californians remain opposed to gay marriage. But polling data indicates that public attitudes are softening.
Opponents have been the target of fierce protests after November's vote. Tomorrow's ruling may arouse renewed anger, but Protect Marriage, the leading group behind the ban, says it is "looking forward" to the decision. "The wait is finally over," read a statement from its general counsel Andrew Pugno. "We're confident that the right of the people to protect traditional marriage in the state Constitution will ultimately prevail."
Timeline: The battle over same-sex marriages in California
February 2004: Gavin Newsom, Mayor of San Francisco, issues an edict allowing gay marriage. But Arnold Schwarzenegger, California's Republican Governor, faces calls from his party to intervene.
March 2004: The state Supreme Court tells San Francisco to halt same-sex weddings, pending a hearing.
August 2004: Nearly 4,000 gay marriages performed earlier in the year in San Francisco are annulled.
September 2005: Governor Schwarzenegger vetoes a bill making California the first US legislature to approve same-sex marriages.
May 2008: The Supreme Court overturns the ban, deciding it is discriminatory.
November 2008: Opponents of gay marriage win the campaign to ban it, known as Proposition 8, with 52 per cent of votes in referendum.
March 2009: Opposition groups file a request for Supreme Court to block the measure, arguing it is unconstitutional. The decision is due on Tuesday.