Just before signing the Defense of Marriage Act into law in 1996, President Bill Clinton said, "I have long opposed governmental recognition of same-gender marriages and this legislation is consistent with that position."

Earlier this month, Clinton said he had changed his mind and now thinks Section 3 of the law defining marriage as between a man and a woman is ­unconstitutional. "We understand that, while our laws may at times lag behind our best natures, in the end they catch up to our core values," he wrote in a Washington Post op-ed.

As the U.S. Supreme Court takes up the issue in the case of U.S. v. Windsor today, it is faced with dozens of briefs from groups of former military officials, intelligence officers and even a bankruptcy judge among others urging it to strike down the law. The question is whether the justices — and especially Anthony Kennedy — will agree with Clinton that the time has come to change course.

"It is unfair to have two classes of marriage and to make same-sex couples second-class citizens," said Roberta Kaplan of Paul, Weiss, Rifkind, Wharton & Garrison, who will argue on behalf of Edith Windsor, who had to pay $363,000 in estate taxes when her spouse, Thea Spyer, died — a tax that opposite-sex married couples don’t have to pay.

Veteran advocate Paul Clement of Bancroft, who will defend the law before the court, says Congress was entitled to define marriage as it chose to for the purpose of allocating federal benefits and programs.

"It does so not by singling out any category of relationships for specific exclusion, but rather by clarifying what marriage means for purposes of federal law," he said. Clement represents the House Republican-led Bipartisan Legal Advisory Group, which stepped in after the Obama administration announced in 2011 that it would not defend Section 3.

Eyeing the national trend

On issues such as the death penalty, the court often takes a headcount of states to see which way the country is trending. On that score, with only nine states and the District of Columbia legalizing same-sex marriage, the outlook may be bleak for those who want to see same-sex marriage given constitutional protection.

Kaplan plans to turn that into an advantage, by focusing on those nine states and arguing that what she is asking the court to do is "not a big deal" — often a winning strategy before a court that likes to take baby steps. She will argue that DOMA should be overturned because of the adverse effect it has on the gay couples who are legally married in those states.

Briefs have identified more than 1,100 statutes where being married in the eyes of the federal government makes a difference — even for those same-sex couples who were legally married.

Opponents of DOMA are also ­hoping that the broad range of support, as reflected in the array of amicus briefs, will persuade the court that erasing DOMA will even the federal playing field without disrupting society, while allowing states to keep or change their marriage laws as they choose.

Take, for example, the brief on behalf of former military officials written by veteran advocate Carter Phillips of Sidley Austin. He argues that treating gay couples equally is an important component of "family readiness," which in turn boosts military readiness. "DOMA threatens the core of the military’s mission and culture," the brief asserts — a remarkable statement, given the military’s general hostility to gays in the not-too-distant past.

"Hopefully, what the amici demonstrate is that the nation has become quite comfortable with gay marriage and with the notion that fundamental fairness dictates not arbitrarily treating those relationships as somehow less deserving in the eyes of the law," Phillips said.

Shotgun weddings

For his part, Clement is advancing another argument that at least one commentator has described as the "shotgun wedding" justification for reserving the institution of marriage for opposite-sex couples only. Clement’s brief notes "the undeniable and distinct tendency of opposite-sex relationships to produce unplanned and unintended pregnancies." That tendency is not a problem for gay couples, he says, because for them, "substantial advance planning is required" to produce a child.

That difference, he continues, makes it rational for government to make marriage unique and attractive for male-female couples only, as a way of encouraging them to raise unplanned children within a marriage. Having unintended children outside of marriage "poses a burden to society," Clement wrote. Patt Morrison, a columnist for the Los Angeles Times, summed up the argument this way: "Shotgun weddings are preferable to gay marriages."

Though this argument is offered as a "rational basis" rationale, some supporters of DOMA view it as a justification that will hold up even if the court adopts a higher level of scrutiny. "It gets us over the heightened-scrutiny hump," said John Eastman of Chapman University School of Law, a key member of the pro-DOMA legal team.

DOMA opponents think they can convince the court to overturn the law under any level of scrutiny, high or low. The difference between same- and opposite-sex couples in terms of their tendency to produce unplanned children, Kaplan’s brief states, is a thin reed on which to justify DOMA.

"This one difference cannot explain the federal government’s decision to impose a sweeping disability on married gay couples that excludes them from countless federal programs, and only harms their children."

Work on the anti-DOMA amicus briefs began last summer with Mary Bonauto, civil rights project director of Gay & Lesbian Advocates & Defenders (GLAD), assuming the lead role of coordinator. Bonauto was well qualified for the task. She and GLAD brought the challenge leading to the landmark Massachusetts Supreme Judicial Court decision in 2003 recognizing same-sex marriage in that state. She also argued and won the first federal appellate court ruling on DOMA: Gill v. Office of Personnel Management.

Said Bonauto, "When you get to the Supreme Court, there is such an outpouring of support. Part of my role is channeling that support. You have to ask: What do the justices really need to hear?"

Coordinate efforts

Unlike the anti-DOMA side, no single member of the pro-DOMA legal team coordinated the amicus briefing, but groups checked in with each other informally to avoid duplication.

Side by side, the amicus briefs present a stark contrast in terms of parties and lawyers representing them. Dominating the anti-DOMA briefs are the nation’s established organizations in the fields of law, history, political science, psychology and sociology as well as libertarian and civil rights groups. There also are briefs by 212 members of Congress, 278 businesses, former cabinet secretaries and military officials. Representing most of those parties are many well-known, veteran Supreme Court advocates from the country’s largest law firms.

Familiar names from the specialized Supreme Court bar are largely missing from the pro-DOMA briefs. Apart from Paul Clement of Bancroft and Chapman’s Eastman, most of the counsel of record may be unfamiliar to the justices or their clerks. "It says a lot about the elite D.C.-New York corridor" that dominates the Supreme Court bar, Eastman said.

Eastman filed a brief on behalf of the Center for Constitutional Jurisprudence, which urges the court to give standing to the Bipartisan Legal Advisory Group "particularly when the President abrogates his duty to ‘take care that the laws be faithfully executed.’ To hold otherwise would give the President a de facto authority to suspend the law, the very concern that the Take Care Clause was designed to protect against." The Justice Department asserts that the bipartisan legal group does not have standing because it suffered no injury.

The court will also hear arguments March 27 on the standing and jurisdictional issues in the DOMA case: whether the bipartisan legal group has Article III standing to defend the law, and whether the Obama administration’s agreement with the lower court’s decision striking down the DOMA provision deprives the justices of jurisdiction to decide the case. The court appointed Harvard Law School professor Vicki Jackson to argue against both jurisdiction and standing. Either issue could derail the case if justices are looking to avoid a landmark ruling, but most lawyers involved in the case think the court will reach the merits.

On the jurisdictional issues, a group of former senior Department of Justice officials and White House counsel, while disagreeing on other issues in the DOMA challenge, said they agree "that this Court is not divested of jurisdiction by the Executive’s decision not to proffer what it considers unreasonable arguments in support of a statute’s constitutionality."

Adds Paul R.Q. Wolfson of Wilmer Cutler Pickering Hale and Dorr, "To the contrary, amici believe that the decision not to defend a statute — under strictly limited circumstances — is a crucial prerogative for the Executive."

The American Sociological Association filed an amicus brief specifically to counter the argument that children fare better with opposite-sex parents than with same-sex parents.

Citing "decades of methodologically sound social science research," Carmine Boccuzzi Jr. of New York’s Cleary Gottlieb Steen & Hamilton wrote, "Whether a child is raised by same-sex or opposite-sex parents has no bearing on a child’s wellbeing."

One pro-DOMA brief that may counter arguments in the brief by former military officials speaks of the "jarring results" for the military of constitutionalizing same-sex marriages. The Chaplain Alliance for Religious Liberty argues that imposing a new definition of marriage on military personnel, especially chaplains, would restrict their religious freedom — and could end their careers, if they object.

"It is very likely that service members who hold traditional religious beliefs on marriage and family will face, for the first time, military policies and duties sharply hostile to their beliefs," wrote retired Army lawyer R. Bradley Lewis of Bogalusa, La.

Tony Mauro and Marcia Coyle write for National Law Journal, a Daily Report affiliate.