As Portlander Thalia Zepatos watched the Supreme Court justices wrestle with gay marriage Tuesday, she was particularly struck by the arguments of the opponents' attorney.

John Bursch, representing the four states fighting to maintain their ban on same-sex marriage, repeatedly argued that the issue wasn't about allowing gay and lesbian couples to express their love and commitment through marriage – it was about keeping kids and their biological parents together.

Zepatos, as a top official for Freedom to Marry, has been encouraging supporters of same-sex marriage to focus on that very issue of love and commitment.

Zepatos helped develop this approach in the wake of ballot defeats in Oregon in 2004 and California in 2008. The change in tactics helped bring the striking increase in public support for gay marriage.

"I just felt that fundamentally we were not having the right conversation," Zepatos said in a phone interview after Tuesday's oral arguments.

Freedom to Marry and other gay-rights groups had once focused on arguing that gays should have the same right to marry as anyone else.

What turned out to be more powerful, she said, was to focus on individual stories of gay couples and how they wanted to get married for the same reasons as straight couples, such as to express their love and commitment and to provide a stable home for their family.

In the lively oral arguments before the court Tuesday – you can read the transcript or listen to an audio recording – Bursch repeatedly tried to turn the justices away from the argument that Zepatos and others used in support of same-sex marriage.

"If you're changing the meaning of marriage from one where it's based on that biological bond to one where it's based on emotional commitment," Bursch said, "then adults could think, rightly, that the relationship is more about adults and not the kids."

Bursch, the former solicitor general of Michigan, added that "when you change the definition of marriage to de-link the idea that we're binding children with their biological mom and dad, that has consequences."

Bursch got plenty of push-back from the liberal wing of the court.

"How does withholding marriage from one group – same-sex couples – increase the value to the other group?" asked Justice Sonia Sotomayer.

More important, Bursch got skeptical questioning from the key swing vote on the court, Justice Anthony Kennedy. He said that same-sex couples understand "the nobility and the sacredness of marriage," and he appeared to cast doubt on Bursch's argument that same-sex marriage could harm "conventional marriage."

Zepatos is not a lawyer, and she acknowledged that she couldn't predict how Kennedy or the court as a whole would rule in the case. After all, at another point in the proceedings, Kennedy expressed concern about changing a definition of marriage that has lasted for so many centuries.

The court's ruling – expected before the end of its term in June – involves four states and would not immediately affect U.S. District Judge Michael McShane's ruling last year striking down Oregon's 2004 voter-approved ban on same-sex marriage.

But John Eastman, chairman of the National Organization for Marriage, said in an interview last week that his group – or other opponents of gay marriage – would certainly file a legal challenge to McShane's ruling if the Supreme Court rules that states are not obligated to allow gay marriage.

Eastman said Tuesday that he was encouraged by Kennedy's comments about how marriage has long been defined as being between one man and one woman.

"It shows that the justices realize that marriage has existed for millennia and they have no constitutional basis to redefine it," Eastman said in a statement.

Zepatos said she finds it hard to believe that the court would try to negate the estimated 400,000 same-sex marriages that have occurred since its Windsor decision two years ago led federal judges around the country to strike down state marriage bans. All told, 36 states and the District of Columbia now allow same-sex marriage.

Zepatos calls herself a "straight ally" of the gay rights movement. She's been involved in Oregon politics since the 1980s, when she worked for the National Abortion Rights Action League. She then fought anti-gay ballot measures sponsored by the Oregon Citizens Alliance and helped found Basic Rights Oregon.

In recent years, she's worked for Freedom to Marry, a New York-based nonprofit that she said will close its doors if the court says gay and lesbian couples have the right to marry anywhere in the U.S.

"I just felt like I had to be here," Zepatos said of her decision to go to Washington for the Supreme Court hearing. "Oregon was sort of the laboratory to figure out this whole messaging.

While the Supreme Court deals with constitutional issues, not political messaging, it was clear from the oral arguments on Tuesday that the line between the two can be blurry.