Gay rights lawyers went to the Supreme Court hoping to find a majority of justices ready to support a historic ruling that would declare same-sex couples had an equal right to marry nationwide.
Instead during Tuesday's arguments, they heard words of hesitation that suggested the outcome is less certain than many expected.
The most important and surprising doubts came almost immediately from Justice Anthony M. Kennedy, who openly wondered whether the court should intervene in an institution so deeply rooted in history and religion.
The word that keeps coming back to me is millennia," Kennedy said in the opening minutes of a 2 1/2-hour argument, prompting looks of concern from gay rights attorneys.
The definition of marriage being limited to a man and a woman "has been with us for millennia," he said. "And it's very difficult for the court to say, 'Oh, well, we know better.'"
Kennedy's apparent struggle over what is perhaps the court's most important civil rights question in a generation was welcomed by state attorneys opposing gay marriage and by his four fellow conservative justices. They emphasized that marriage has been limited throughout American history to a man and a woman, and that the issue is better left to voters at the state level, rather than to federal judges.
Despite his comments, Kennedy — who will probably have the deciding vote — may still rule in favor of marriage rights for same-sex couples when the court announces its decision in June. Kennedy in the past had similarly voiced doubts during an argument, only to discard them when the time came to make a decision.
More important, Kennedy has written the court's three important rulings in favor of gay rights, including an opinion two years ago that spoke glowingly of the "equal dignity" of same-sex couples who had married. It was that decision that led to a string of rulings by federal courts over the last year that invalidated states' same-sex marriage bans as unconstitutional.
To the relief of gay rights advocates, Kennedy later in Tuesday's argument returned to some of his more familiar themes about equality and at one point chided a Michigan state lawyer for insisting that marriage was chiefly about biology and procreation, and not recognizing the dignity derived from being in a committed couple.
"Same-sex couples say, 'Of course, we understand the nobility and sacredness of the marriage. We know we can't procreate, but we want the other attributes of it in order to show that we too have a dignity that can be fulfilled,'" Kennedy said.
With an estimated 250,000 children that are being raised by same-sex couples across the nation, Kennedy also questioned the harm same-sex marriage bans have on such families.
Kennedy's colleagues seemed less ambivalent about the question before them.
The court's four most conservative justices, including Chief Justice John G. Roberts Jr., left little doubt they would vote to uphold the state bans on same-sex marriage. Roberts said gay rights proponents were seeking to redefine marriage.
"You're not seeking to join the institution," he told attorney Mary L. Bonauto, who is representing two Michigan nurses who have been unable to marry and jointly adopt the four abandoned foster children they are raising. "You're seeking to change what the institution is."
Roberts also warned that a ruling from the high court at this time would prematurely shut down the national debate over the issue.
But Bonauto emphasized that the rights of gays and lesbians were being compromised in many states and that it was unfair to tell gay couples to "wait and see."
The four liberal justices said they saw no valid legal justification to deny marriage to same-sex couples, questioning how such recognition would harm heterosexual marriage.
"We are not taking anyone's liberty away" by allowing gay couples to marry, said Justice Sonia Sotomayor.
They attacked the argument that marriage is intended chiefly to encourage child-rearing, and noted that many heterosexual spouses do not have children and a growing number of same-sex couples do, either through adoption or surrogacy.
Justice Stephen G. Breyer said the court had repeatedly ruled that Americans have a fundamental right to marry, and he questioned whether "purely religious reasons" can justify a ban on same-sex marriage.
"There is one group of people whom [some states] won't open marriage to," Breyer said. "So they have no possibility to participate in that fundamental liberty. That is people of the same sex who wish to marry. And so we ask, why? And the answer we get is, 'Well, people have always done it.' You know, you could have answered that one the same way we talk about racial segregation."
U.S. Solicitor Gen. Donald Verrilli Jr., representing the Obama administration, made a brief but powerful argument in favor legalizing gay marriage.
"In a world in which gay and lesbian couples live openly as our neighbors, they raise their children side by side with the rest of us, they contribute fully as members of the community, it is simply untenable, untenable to suggest they can be denied the right to equal participation" in marriage, he said.
They should not "be required to wait until the majority decides it is ready to treat gays and lesbian people as equals. They deserve the equal protection of the laws, and they deserve it now," he said.
The debate over gay marriage was largely unthinkable just a decade ago, when only one state permitted gay marriage, public opinion was solidly against it and Republicans used state referendums banning same-sex unions to bolster conservative voter turnout in the 2004 presidential race.
Today, public opinion polls show a majority of Americans support gay marriage and it is legal in 37 states because of court rulings or state laws.
Aware of the social and political sensitivities, the court had attempted to move slowly on the issue. Presented with the chance to rule on gay marriage in 2013, the majority instead took a smaller step, striking down part of the federal Defense of Marriage Act and declining to declare same-sex marriage a constitutional right.
The 2013 decision, written by Kennedy, fueled a string of court challenges over gay marriage, mostly decided in favor of allowing same-sex unions. When the U.S. 6th Circuit Court of Appeals bucked the trend by upholding statewide bans against gay marriage, the high court was compelled to revisit the question.
The justices will meet Friday to discuss the cases and cast their votes. They must decide whether to uphold gay marriage bans in four states — Michigan, Ohio, Kentucky and Tennessee — or strike them down as unconstitutional, thereby legalizing gay marriage nationwide.
A third option is before them as well. They could rule that there is no constitutional right to gay marriage, but that states must recognize the same-sex marriages of other states, even if they ban the practice themselves. Such a ruling would make gay marriage widely available, without establishing it as a constitutional right.
That was the focus on the second part of the argument, but none of the justices sounded attracted to that middle-ground position.