Now that today’s Supreme Court arguments over Proposition 8 have concluded, the broad consensus among legal observers is that a narrow ruling looks more likely. But gay rights advocates believe this is a premature judgment — and that a broad Constitutional ruling remains a real possibility.

The prediction of a narrow ruling is based on two lines of questioning from conservative Justices, both of which suggested discomfort with moving the country forward too quickly on gay marriage. The one that’s getting the most attention, from crucial swing vote Anthony Kennedy, asked whether a broad ruling would mean SCOTUS is heading into “uncharted waters.” The other, courtesy of Samuel Alito, asked whether not enough is known about the societal impact of gay marriage to justify quick action legalizing it.

The prospects for a broad ruling hinge partly on whether the Justices, particularly Kennedy, decide that opponents of Prop 8 — Ted Olson and Solicitor General Donald Verrilli — effectively answered these concerns.

Again and again, Olson repeated that the Court had previously found a “right” to marry, irrespective of procreative intent, in keeping with the plaintiffs’ broad argument that marriage is a Constitutional right. Olson cited Loving v. Virginia, which struck down a ban on interracial marriage on the grounds that excluding citizens from the right to marry deprives them of liberty without due process. I particularly liked Olson’s closing, which linked this concept to a rebuttal of Kennedy’s “uncharted waters” line and a broad reading of American history as a continual extension of liberty to previously excluded groups:

“You suggested that this is uncharted waters. It was uncharted waters when this Court, in 1967, in the Loving decision, said that prohibitions on interracial marriage, which still existed in 16 states, were unconstitutional.”

Olson closed by quoting language previously used by Justice Ruth Bader Ginsburg: “A prime part of the history of our Constitution is the story of the extension of constitutional rights to people once ignored or excluded.”

Verrilli made a somewhat narrower argument, but still a Constitutional one: that Prop 8 merits “heightened scrutiny” which reveals it to violate the Constitution’s equal protection clause. He, too, reached back to Loving v. Virginia to rebut the Justices’ worry about moving too quickly, pointing out that exactly the same argument had been made by foes of interracial marriage.

“Waiting is not a neutral act,” Verrilli said. “Waiting imposes real costs in the here and now. It denies to the parents who want to marry the ability to marry, and it denies to the children, ironically, the very thing that Petitioners focus on as at the heart of the marriage relationship.” By which he meant: Stability.

“The principle argument in 1967 with respect to Loving and that the Commonwealth of Virginia advanced was: Well, the social science is still uncertain about how biracial children will fare in this world,” Verrilli continued. “I think the Court recognized that there is a cost to waiting and that that has to be part of the equal protection calculus.”

It is hard to know whether the Justices — Kennedy in particular — were signaling insurmountable concerns with their questions or whether they were giving Prop 8 opponents an opportunity to address those concerns. If it’s the latter, a broad ruling is still possible.

“We’re asking the Supreme Court to do a very big thing, so it’s natural that they would have some issues and some difficulty wrapping their heads around them,” Socarides told me. “I’m still optimistic that we’re going to get five votes for a Constitutional ruling in this case.”

The continual links back to Loving v. Virginia are a reminder of just how momentous today’s arguments really were. We just saw the case for full equality for gays linked directly to the nation’s other great civil rights struggles before the highest court in the land. Such a thing would have been unthinkable only a decade ago, and it alone was a historic moment, standing out against the backdrop of a culture which — whatever the court rules in this case — is moving inexorably towards a just outcome for gay and lesbian Americans.

Greg Sargent writes The Plum Line blog, a reported opinion blog with a liberal slant -- what you might call “opinionated reporting” from the left.