Perhaps bowing to political caution in an election year, the president added, "I had hesitated on gay marriage in part because I thought that civil unions would be sufficient. I was sensitive to the fact that for a lot of people, the word marriage was something that invokes very powerful traditions and religious beliefs."
The message was reaffirmed in broad strokes at the January inaugural address: "Our journey is not complete until our gay brothers and sisters are treated like anyone else under the law -- for if we are truly created equal, then surely the love we commit to one another must be equal as well."
Differences along generational lines
A new national survey indicates a growing majority of Americans backs such marriages, but that there are major generational and partisan divides, as well as a gender gap. According to a CNN/ORC International poll from mid-June, 55 percent of the public believes marriages between gay or lesbian couples should be legally recognized as valid, with 44 percent opposed.
"There are big differences among younger and older Americans, with the youngest age group twice as likely as senior citizens to support same-sex marriage," says CNN polling director Keating Holland. "Women are also more likely to call for legal recognition of gay marriage than men. And only three in 10 Americans who attend religious services every week support same-sex marriage while six in 10 Americans who don't attend church weekly feel that way."
Such support for gay and lesbian marriages was only 44 percent just four years ago.
Former President Bill Clinton, who signed DOMA into law 17 years ago, said in March he now backs the right of homosexuals to marry.
So, too, his wife, former Secretary of State Hillary Clinton. Prominent conservatives who support it include actor/director Clint Eastwood; former Vice President Dick Cheney, whose openly lesbian daughter Mary married her longtime partner last year; and Sen. Rob Portman, R-Ohio, who told CNN recently his change of heart came after his 21-year-old son came out as gay.
But others on the right say society benefits from preserving a view of marriage that has been in place for centuries.
The authors of a new book, "What is Marriage? Man and Woman: A Defense," say, "Redefining marriage would, by further eroding its central norms, weaken an institution that has already been battered by widespread divorce, out-of-wedlock child bearing and the like."
Academics Robert George, Sherif Girgis and Ryan Anderson say marriage should be more than "commitment based on emotional companionship," and has been practiced for a specific reason throughout this country's history.
"All human beings are equal in dignity and should be equal before the law. But equality only forbids arbitrary distinctions," they argue. "And there is nothing arbitrary about maximizing the chances that children will know the love of their biological parents in a committed and exclusive bond. A strong marriage culture serves children, families and society by encouraging the ideal of giving kids both a mom and a dad."
Will ruling be broad or narrow?
The last piece of this political mosaic -- the most immediate element in the call for binding clarity in the same-sex marriage debate -- comes from the highest court in the land.
The DOMA and Prop 8 cases will test the delicate line over constitutional limits from congressional, presidential and judicial power.
All nine justices have had a significant voice in both oral argument and Wednesday's rulings, but it may be one member of the court whose views may count most in the high-stakes quest for five votes -- a plurality ensuring victory.
Justice Anthony Kennedy authored the landmark 1996 Romer v. Evans decision, striking down a Colorado constitutional amendment that forbid local communities from passing laws banning discrimination against gays.
The moderate-conservative wrote for the 6-3 court majority, rejecting the state's argument the law only blocked gay people from receiving preferential treatment or "special rights."
"To the contrary, the amendment imposes a special disability upon those persons alone," said the 76-year-old Kennedy. "Homosexuals are forbidden the safeguards that others enjoy or may seek without constraint."
In dissent, Justice Antonin Scalia criticized the court for placing what he said was "the prestige of this institution behind the proposition that opposition to homosexuality is as reprehensible as racial or religious bias."
In 2003, Kennedy authored the court's decision overturning state laws criminalizing homosexual sodomy. At the time though, he cautioned the court was not endorsing the idea of same-sex marriage, saying the private conduct case at hand "does not involve whether the government must give formal recognition to any relationship that homosexual persons seek to enter."
That caution was further articulated in a March speech by Kennedy, when he said some issues are best left to the other branches. "I think it's a serious problem. A democracy should not be dependent for its major decisions on what nine unelected people from a narrow legal background have to say," he said.
By patiently letting legislatures and the voters decide the social and practical implications of same-sex marriage over the past decade, the high court is now poised to perhaps offer the final word on tricky constitutional questions. Or not.
The split 5-4 conservative-liberal bench has the option of ruling broadly or narrowly -- perhaps taking a series of incremental cases over a period of years, building political momentum and public confidence in the process.
The Prop 8 case is Hollingsworth v. Perry (12-144). The DOMA case is U.S. v. Windsor (12-307).