Photograph by Kathryn Maloney / Getty

The fight to bring marriage equality to all fifty states heads to the Supreme Court again later this month, with an extraordinary two and a half hours of oral argument set for the morning of Tuesday, April 28th. The four cases before the Court deal with marriage bans in Ohio, Michigan, Kentucky, and Tennessee. But their potential repercussions are much broader.

Two years ago, the Court struck down the federal Defense of Marriage Act (DOMA) in the landmark case of United States v. Windsor, where it held, in broad language, that Congress could not deny federal recognition to same-sex marriages performed in states that permit them. Now marriage-equality activists hope that the Court will extend the Windsor rationale and language into a rule that requires every state to allow gays to marry. Most observers expect that it will, and that the impact of such a ruling will eventually extend beyond marriage rights, transforming how gay Americans are perceived and reducing discrimination against them more broadly.

With the Court seemingly on the verge of an historic precedent, the selection of the lawyers for oral argument became a point of some contention among the many attorneys involved in the various cases.

During a confidential selection process that included a “moot-off” (essentially Supreme Court auditions), lawyers for all of the plaintiffs agreed on Mary Bonauto—who argued the first successful gay-marriage case, in Massachusetts, in 2003, and who has been one of the leading advocates for the cause since its inception—as their main advocate before the high court. She will argue on the central question framed by the Court: “Does the Fourteenth Amendment require a State to license a marriage between two people of the same sex?" Although a leading advocate for marriage rights, Bonauto has never argued a case before the U.S. Supreme Court. She will tell the Justices that marriage restrictions deny gay Americans their right to equal protection of the law and that such statutes also deprive them of a core liberty protected by the due-process clause of the Constitution.

Joining Bonauto will be a veteran Washington and Supreme Court litigator, Douglas Hallward-Driemeier, who will argue on the second question the Court has framed: "Does the Fourteenth Amendment require a state to recognize a marriage between two people of the same sex when their marriage was lawfully licensed and performed out-of-state?" An affirmative answer on the first question would seem to render the second moot.

The U.S. Solicitor General Donald B. Verrilli, Jr., will argue, on behalf of the government, for a fifty-state marriage rule. This is a broader position than the government took two years ago, when it argued against DOMA but for a more incremental approach to the marriage question itself. (It argued then, convolutedly, that only states that grant legal recognition to gay relationships should be forced to grant marriage rights.) The government’s position has strengthened as support for marriage equality has increased nationally, and as the Administration has seemed to recognize that the issue resonates with its political supporters.

Arguing against marriage rights will be John Bursch, a former Michigan solicitor general, and Joseph Whalen, a Tennessee associate solicitor general. All four states are defending their marriage prohibitions.

In the two years since the Court last faced this issue, the nation has seen unprecedented political and cultural changes in attitudes toward same-sex marriage. In 2013, when, alongside the DOMA challenge, the lawyers Ted Olson and David Boies argued their challenge to California’s Proposition 8, which banned same-sex marriage in that state, only nine states allowed gay marriage. The case was ultimately successful in bringing marriage rights back in California, but the Court ruled on procedural grounds, which limited the decision’s scope, and many marriage-equality advocates argued that Boies and Olsen had been too quick to bring the issue before the Court. “In hindsight, Boies and Olson have been vindicated,” the law professor and gay-rights scholar Kenji Yoshino writes in his forthcoming book about the case, “Speak Now,” in that they prepared the Court and the public for subsequent cases.*

Now the number of states allowing gay marriage is up to thirty-seven. These legal changes have been accompanied by, and are perhaps the results of, accelerating acceptance of gays and lesbians and increasing support for marriage rights. The most recent polling shows that over sixty per cent of Americans now support marriage equality. Evan Wolfson, the founder of the group Freedom to Marry, pointed out to me that “some of the Justices who voted against us” in Windsor did so on the grounds “that there was something so ‘novel’ or ‘untested’ or still ‘in doubt’ ” about gay marriage. That is no longer the case.

These broad changes in public opinion were on display last week in Indiana and Arkansas, where the business community—not known as a bastion of progressive activism—rallied against laws that would have allowed businesses, based upon their religious beliefs, to refuse service to gay and lesbian customers. Those laws were intended by their sponsors to be a sort of consolation prize to the religious right, which, like everyone else, expects the Supreme Court to rule in favor of a nationwide right to same-sex marriage.

While no Supreme Court ruling can be considered a forgone conclusion, it seems as though the main suspense about the outcome is how many votes same-sex marriage will garner. In an e-mail this past weekend, Olson told me that he was “heartsick about being on the sidelines as this so very important issue moves to a climax in the Supreme Court.” But he added, “I feel deeply committed to this issue . . . at what I hope and expect to be the finish line.” With respect to the outcome, Olson says, “I wish, like Loving” (meaning Loving v. Virginia, in which the court struck laws against interracial marriage), “it could be 9-0, but I suspect that is not in the cards. I would hope that it would be more than 5-4, as this means so much to this country and our values.”

This is a huge moment for gay Americans. A major civil-rights victory, once thought unimaginable in our lifetime, is likely upon us. As Dustin Lance Black, the Academy Award-winning screenwriter of the movie “Milk” and a co-founder of the organization that brought the Prop 8 legal challenge (Black also wrote a play, “8,” about the case) told me, “Growing up in Texas, I learned that the way to earn respect was to treat myself with respect, to stand up for myself. That is exactly what the L.G.B.T. movement started to do again after Prop 8's passage in California in 2008.” It was also the moment when a backlash against the unfairness of such laws finally started to take hold in America. Six years later, the Supreme Court appears ready to endorse not only same-sex marriage, but full legal equality for all gay Americans.

*Correction: A previous version of this post misspelled Kenji Yoshino’s name.