Among the many documents that Supreme Court justices have to consider when deciding a case, amicus briefs are generally predictable and inconsequential: they come from groups who advocate a long-held position but aren't directly involved in the arguments.
Then there's the one being drafted by a group of prominent Republicans in support of gay marriage.
This particular amicus brief exposes a growing fissure within the GOP and could arguably influence the thinking of one or more of the justices, who are considering two cases that could determine whether bans on gay marriage are legal, experts say.
The New York Times reported Tuesday that dozens of current and former GOP leaders, including two members of Congress, four ex-governors and the former chairman of the Republican National Committee, are preparing to submit an amicus (friend-of-the-court) brief this week arguing that Proposition 8, a California law prohibiting same-sex marriage, should be toppled.
The move contradicts the party's official position and defies House Republicans, who in a separate case took up the defense of a federal law denying benefits to same-sex spouses after President Barack Obama chose not to.
The high court is scheduled to begin hearing arguments on the California and federal laws next month.
The Republican group's new brief will say that same-sex marriages promote the conservative ideals of strong family values and individual freedom, according to the Times.
That would be a twist on the traditional Republican argument for limiting marriage to a man and a woman.
It would also present another sign that opponents of gay marriage are becoming the minority.
Polls show that Americans are increasingly accepting of gay marriage. The number of states where it is legal has grown to nine, with five more allowing civil unions and three — including California — permitting domestic partnerships. Last spring, Obama announced that he'd changed his mind and now felt comfortable with same-sex marriage. He highlighted the issue in his inaugural address last month, and may submit his own amicus brief on the Proposition 8 case.
Many legal experts say it is inevitable that bans on same-sex marriages will be eliminated from American life.
So the Republicans' amicus brief can be seen as an effort to nudge the GOP—and the high court—to the right side of history.
Supreme Court justices tend not to want to take a position on a case that could soon be considered obsolete.
"The justices aren't unaware that attitudes on this issue are changing rapidly," said G. Edward White, a professor at the University of Virginia School of Law and a scholar of Supreme Court history.
"They have to think about that: do they want to be associated with a position that's going to be overruled? In that context, the fact that these prominent conservative politicians put their names on a brief in support of same-sex marriage is a little bit of a signal. These people, who are in the business of reputational currency, have concluded that the thrust of politics is going to be in favor of this, and (the justices) should get on board."
Jane Schacter, a constitutional law expert at Stanford Law School, said the power of the Republicans' amicus brief lies in the fact that many of the people who have reportedly signed it are people who have argued against the legality of same-sex marriage in the past. As people get used to the concept, the arguments against it "kind of evaporate and start to look like a pretext for discrimination rather than rational policy reasons."
In the end, the central argument becomes: what is the compelling legal reason to keep same-sex couples from marrying? Tradition, Schacter said, isn't enough.
"Justices don't want to be seen as the last gasp of a kind of retrograde resistance to this kind of idea when things are moving so quickly," she said.
The Republicans' filing has the potential of being the most influential amicus brief since 29 retired military officers weighed in on a 2003 Supreme Court decision on affirmative action at the University of Michigan, Schacter said. The court ruled in favor of the policy, and cited the officers' brief.
Among those who have reportedly signed the Republican amicus brief are Rep. Ileana Ros-Lehtinen of Florida, Rep. Richard Hanna of New York, former Utah Gov. Jon Huntsman, former New Jersey Gov. Christine Todd Whitman, former Massachusetts Govs. William Weld and Jane Swift, former Republican National Committee chairman Ken Mehlman, who is openly gay, and several former advisers to former President George W. Bush.
They will effectively join forces with another prominent conservative, Ted Olson, former President George W. Bush's solicitor general and a lead lawyer for the group seeking to overturn California's ban.
Several of the co-signers, including Huntsman, had previously spoken in opposition to gay marriage.
"I think that this is one of those…unusual situations where the justices will certainly notice the signatories on this brief," White said.
Many Supreme Court observers predict that eight of the nine justices will be divided on the issue, with Justice Anthony Kennedy representing a swing vote. He was presumably the main target of the amicus brief.
"The fact that more and more Republicans are coming out in favor of gay marriage simply confirms how dramatic the shift in public opinion has been — and that is a fact that likely is of great significance to Justice Kennedy," Michael Klarman, a Harvard Law School professor and author of “From the Closet to the Altar: Courts, Backlash and the Struggle for Same-Sex Marriage,” told NBC News in a email.
But White said he will also be looking at two other right-leaning members of the court, Chief Justice John Roberts and Justice Samuel Alito, as possible wild cards.
In that scenario, a one-sided decision seems more plausible.
Just how much they will be influenced by the Republicans' brief is impossible to know.
"I'd say it might have some weight," White said. "I doubt very much that a particular justice will say, 'I was going to go the other way, and then I saw that the few Republican politicians had signed on.' But it's a reminder that the issue is changing rapidly in the direction of support of gay marriage."