KING: California's legal battle over same-sex marriage dates back to February 2004, when San Francisco Mayor Gavin Newsom authorized the city clerk to issue marriage licenses to same-sex couples. Since then, the battle has taken a dizzying number of twists and turns through California's courts.

Last year, the state Supreme Court overturned a voter-approved ban on same-sex marriage. Yes, that's the same court that today upheld Proposition 8.

"Digging Deeper," let's bring in Mayor Gavin Newsom of San Francisco.

Mayor, the court's decision today was 6-1.

GAVIN NEWSOM (D), MAYOR OF SAN FRANCISCO: Yes.

KING: The decision last year granting the right to marry was only 4-3. How big of a setback is this to proponents of same-sex marriage?

NEWSOM: I don't know that it's a huge setback.

I mean, candidly, most of the pundits, most of the people I talked to privately, candidly, expected the decision. It, nonetheless, was a very disappointing decision and one that we will have to recover from, because, remember, John, we now no longer have a court we can count on. We can't count on the legislature. We can't count on the executive branch.

At the end of the day, the only people we with count on are ourselves, the voters of California, which means we have to go right back to those same voters that rejected at least our point of view as it relates to marriage equality just last year.

KING: You say right back to those voters. Do you believe you should do that in 2010, or do you need time to get it right this time, in your view?

NEWSOM: Good people can disagree. As Dr. King said -- I will paraphrase -- wait almost always means never. It's always the right time to try to do the right thing.

I think it is the right time. The world has changed dramatically from last November. People's focus is elsewhere. To the extent that this is an emotional issue, it is. But I also think the opportunity to right some of the wrongs of that last campaign and organize a much more effective grassroots campaign is upon us. So, I think next year makes a lot of sense.

KING: Let me read you something from the majority decision today. The court said: "Proposition 8 does not entirely repeal or abrogate the aspect of a same-sex couple's state constitutional right of privacy and due process. Instead, the measure carves out a narrow and limited exception to these state constitutional rights, reserving the official designation of the term marriage for the union of opposite-sex couples as a matter of state constitutional law."

So, some could say the court has left open the possibility of essentially civil unions with just about all the benefits and advantages, just not the term marriage. What would be wrong with that?

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NEWSOM: Well, I know who difficult that is. I have family members that say, can't we just call it something else? And I understand that probably a majority of Americans believe that, good people.

At the end of the day, though, it's also the 55th anniversary of Brown vs. the Board of Education. Separate is not equal. Civil unions are civil unions. Marriage is marriage. They're different institutions.

KING: As you prepare to go back at this battle again in California, Iowa has acted. There's a proposal here in New York State.

NEWSOM: Yes.

KING: There's a proposal in New Hampshire. Maine has acted. On this day, when President Obama made his first pick for the United States Supreme Court, lay out for me what you see as the national constitutional issue and how you see this issue.

NEWSOM: Yes.

KING: I assume you agree, someday, and someday soon, probably coming before the nation's highest court.

NEWSOM: Well, I think it's a great question and well-framed.

The history, for example, of interracial marriage began in California in the late 1940s. It ultimately worked its way up to the U.S. Supreme Court in 1967 in the famous Loving vs. the State of Virginia case.

It's inevitable that that's the same narrative of this. So, it is interesting, isn't it, today, when we have a new nominee to that court who most likely will see this case ultimately in her future, if she's finally appointed and confirmed.

KING: Mayor Gavin Newsom, thanks for your time tonight.

NEWSOM: Thank you, John.