SAN FRANCISCO (KCBS)— The man who many credit with kicking off the same-sex marriage movement by issuing marriage licenses in San Francisco says he’s optimistic about an end to bans on same-sex marriage.

Both sides of the issue argued their case to the U.S. Supreme Court on the gay-marriage restrictions in four states on Tuesday. The final ruling in the case could legalize same-sex marriage nationwide.

Full Transcript: Supreme Court Same-Sex Marriage Hearing

Lieutenant Governor Gavin Newsom who, as San Francisco Mayor in 2004, directed City Hall to issue same-sex marriage licenses, attended the arguments in Washington D.C.

“At the end of the day I feel pretty optimistic having sat through not only this court and the oral arguments but in 2013, the Windsor arguments were frankly, I felt, less optimistic though it turned out favorably,” said Newsom, referencing the case that struck down the Defense of Marriage Act two years ago.

KPIX5 Legal analyst Melissa Griffin-Caen says it appears that the four conservative justices are lining up against same sex marriage and the 4 liberal ones for it.  Justice Kennedy appears to be the swing vote, and some saw a potentially bad omen when Kennedy spoke about his concerns on redefining marriage.

“This definition has been with us for Millennia and it’s very difficult for the court to say “we know better,” Justice Kennedy said. “I don’t think it’s a question of the court knowing better. Think about the debate, about the place of gay people in our civic society.  It’s something that has been contested for more than a century.”

However, when the lawyer for the state of Michigan told the court same sex marriage would hurt heterosexual families.  Kennedy seemed to refute that.

“Same-sex couples say, of course, ‘we understand the nobility and the 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.

Full Audio: US Supreme Court Hearing On Same Sex Marriage

CBS News Senior Legal Analyst Andrew Cohen spoke with KCBS saying the obvious argument on one side is that the definition of marriage should be an issue that’s decided upon by the state.

“Kennedy – who’s going to be the swing vote, who’s going to be a big supporter of state’s rights and a big supporter of gay rights – he’s going to have to pick between one of those two things as the case goes forward,” Cohen said. “There are two issues. There’s the same-sex marriage ban issue, whether or not they’re constitutional and then there’s the recognition issue, whether a state has to recognize same-sex marriages that takes place in a neighboring or other state. If the justices can offer clarity one way or another on that, then we can finally have this issue move past the courts. It’s been there for 10 years.”

Two years ago the U.S. Supreme Court dodged the issue a bit when they dismissed an appeal of the Proposition 8 decision, but in doing so, Cohen said it brought forth a whole new set of legal issues.

“Since the Prop. 8 decision and the Federal Defense of Marriage Act decision, most of the federal judges who have looked at those decisions have decided that the Supreme Court meant to outlaw or to ban the bans. That’s why you’ve seen one federal judge after another, circuit after another, saying that same sex marriage has to be lawful. There are exceptions of course and it’s the exception that one federal circuit that creates the conflict among the circuit that requires the Supreme Court intervention.”

Cohen said the folks who oppose same-sex marriage say there’s a rational basis for it and that there are reasons for separating different classes of people for different treatment. Of course those who are opposed to the bans say that’s nonsense. It violates the equal protection rights of all people when same-sex people are denied the same privileges that opposite-sex couples get through marriage.

Some law experts say the four liberal justices are aligning in favor of the equal protection clause; requiring states extend marriage to same-sex couples. The four conservatives are lining up against again with Justice Kennedy’s vote potentially settling the law.