(CNN) -- "Marriage is a coming together for better or for worse, hopefully enduring, and intimate to the degree of being sacred. It is an association that promotes a way of life, not causes; a harmony in living, not political faiths; a bilateral loyalty, not commercial or social projects." -- Supreme Court's 1965 ruling in Griswold v. Connecticut
President Barack Obama once believed marriage only was for one man and one woman.
He then backed civil unions for gay and lesbian couples, granting them many of the same rights and privileges as married heterosexuals.
Now he is firmly in support of a constitutional right that has put him at odds with many social conservatives.
It is a personal and political evolution that in many ways reflects the country as a whole. Shifting public opinion and decades-old fights over judicial power are at the nexus of perhaps the most important social issue the high court has addressed in recent years: same-sex marriage.
Rulings in two separate cases are expected from the U.S. Supreme Court on Wednesday morning.
There are about 120,000 legally married same-sex couples in the United States. Many thousands more seek the same thing. But it may be 10 people who have the power to force immediate, real change on this legal, political, and social issue: the nine justices and Obama himself.
What the highest officers of all three branches have said -- and more importantly how they will act this week and beyond -- could set the template for years to come on a contentious topic that shows no sign of cooling.
"The argument that the Obama administration has made is the Supreme Court should look at these laws very carefully because gays and lesbians are a group that have been subject to discrimination in the past," said Amy Howe, a legal analyst and editor of SCOTUSblog.com, "'and will be subject to discrimination going forward. So the Supreme Court would need to subject these laws to what we call a very stringent standard of review" balancing the government's justification for enacting them.
One side of issue has some momentum
Two separate appeals -- challenges to a state and federal law -- once again will put the high court at the center of national attention, a contentious encore to its ruling exactly a year ago upholding the massive health care reform law championed by Obama.
Ten states allow same-sex marriage, three just since November when voters blessed it: Washington, Maryland, and Maine -- along with Iowa, New Hampshire, Vermont, Massachusetts, Connecticut, New York, Rhode Island, as well as the District of Columbia. Minnesota and Delaware will join the ranks in coming weeks.
But 36 states have specific laws blocking gays and lesbians from legally marrying, a point made by "traditional" marriage supporters when dismissing any nationwide social momentum toward acceptance of homosexuals being allowed to wed.
The cases the high court is poised to decide:
-- Federal benefits. The Defense of Marriage Act or DOMA is a 1996 congressional law that says for federal purposes, marriage is defined as only between one man and one woman. That means federal tax, Social Security, pension and bankruptcy benefits, family medical leave protections -- and a thousand more such provisions-- do not apply to gay and lesbian couples, such as Edie Windsor. The 84-year-old New York woman is the key plaintiff in the DOMA fight, forced to pay more than $363,000 in extra estate taxes when her longtime spouse Thea Spyer died.
-- State referendums. The California high court had earlier concluded same-sex marriage was legal, but the 2008 voter-approved Proposition 8 abolished it. The high court is being asked to establish same-sex marriage as a constitutional right, but could also decide a more narrow question: whether a state can revoke that right through referendum once it has already been recognized.
Obama: No more hesitation on my stance
Running for the Illinois state senate in 1998, Barack Obama said he was "undecided" on whether to legalize same-sex marriage. Fast forward six years.
"What I believe is that marriage is between a man and a woman." That was U.S. Senate candidate Obama in 2004. "What I believe, in my faith, is that a man and a woman, when they get married, are performing something before God, and it's not simply the two persons who are meeting."
His stance at the time disappointed many in the Illinois LGBT community, but it began an internal process over time that was by his admission, anything but smooth.
"My feelings about this are constantly evolving. I struggle with this," he said in 2010, two years into his presidency. He told Jake Tapper, now anchor of CNN's "The Lead," that "at this point, what I've said is, that my baseline is a strong civil union that provides them the protections and the legal rights that married couples have."
Gay rights groups had privately urged Obama and his top aides over a period of many months to go beyond his previous personal rhetoric in support of the marriage right, and come down "on the side of history" in this legal struggle.
Government sources told CNN that Obama made the final decision to file the Supreme Court briefs in the current cases, and the legal language to use.
This was all set in motion in the heat of the president's re-election campaign last year.
In what government sources says was a quickly-arranged political strategy, Obama told ABC News, "At a certain point, I've just concluded that for me personally it is important for me to go ahead and affirm that I think same-sex couples should be able to get married."
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% of the public believes marriages between gay or lesbian couples should be legally recognized as valid, with 44&% 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% 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).