WASHINGTON, DC — In what amounts to a direct challenge to Speaker John Boehner and the conservative leadership of the U.S. House of Representatives, dozens of prominent Republicans, including several with senior ties to former President George W. Bush, have signed a legal brief in support of the constitutional right of gay Americans to marry.

The document, which was also signed by four former state governors and two Members of Congress, reflects the growing rifts in the national Republican Party since its defeat in the November 2012 presidential election.

It will be submitted this week to the U.S. Supreme Court as an amicus (or “friend of the court”) brief in support of a lawsuit challenging Proposition 8, the California voter-approved ballot initiative that bans same-sex marriage, as well as all other similar prohibitions.

The high court will hear that challenge next month, along with a suit seeking to overturn the Defense of Marriage Act (DOMA), the 1996 federal law that defines marriage as between one man and one woman. The justices are expected to deliver a decision sometime in June.

Experts say the brief has the potential to influence conservative justices in equal measure because of the legal arguments contained as well as for the influential names attached to it.

As of February 25, the names of current and former GOP officials, grandees, and ideologues included 75 individuals not normally associated with LGBT rights activism.

Meg Whitman, an unsuccessful Republican candidate for Governor of California who supported Proposition 8, signed the brief, changing her previous position. Others who signed include Stephen Hadley, a National Security Adviser under George W. Bush, Bush Commerce Secretary Carlos Gutierrez, David Stockman, Director of the Office of Management and Budget under Ronald Reagan, U.S. Rep. Ileana Ros-Lehtinen (R-Miami), and Ken Mehlman, the former Chairman of the Republican National Committee (RNC), who came out in August 2010, which made him one of the most prominent openly-gay figures in the Republican Party.

Mehlman serves on the board of the American Foundation for Equal Rights, which brought the Proposition 8 suit. Reports have him spending the past several months lobbying fellow Republicans to garner support for the brief.

Former governors Jane Swift (Massachusetts), William Weld (Massachusetts), Christine Todd Whitman (New Jersey), and Jon Huntsman, Jr. (Utah) also signed. Huntsman—who supported civil unions but opposed gay marriage during his unsuccessful 2012 GOP presidential bid—last week wrote an article (“Marriage Equality Is a Conservative Cause”) in which he likewise re-examined his earlier opposition. (See the related story in this week’s Agenda NATION section, Page 11).

The Proposition 8 case already enjoys the backing of Theodore Olson, the former Bush Solicitor General who is also one of the suit’s two lead attorneys.

The brief—which was written by Reginald Brown, who worked in the Office of White House Counsel under George W. Bush and Seth Waxman, a Solicitor General under President Bill Clinton—contends that marriage equality fosters family values by allowing the children of same-sex couples to grow up in two-parent homes, advancing traditional (and conservative) values that include “limited government and maximizing individual freedom.”

This stands in stark contrast to the language contained in the RNC official platform, which supports amending the U.S. Constitution to define marriage as “the union of one man and one woman.”

The brief cites prior Supreme Court decisions that are popular with conservatives, including the 2010 Citizens United v. Federal Election Commission ruling that lifted campaign financing restrictions, and District of Columbia v. Heller, a 2008 Second Amendment ruling that overturned a law prohibiting handgun ownership.

The signers of the legal brief have placed themselves squarely against Boehner and rest of the House Republican leadership, which has approved the expenditure of tax dollars to defend DOMA.

In turn, those House leaders find themselves increasingly going against public attitudes towards marriage equality, which polls suggest have shifted dramatically in just the past 10 years.

In 2003, roughly a third of Americans said they supported same-sex marriage; today a majority favor it, while recent polls indicate that roughly 70 percent of voters under 30 years old support gay marriage. The strongest opposition is to be found in the geographic South.

Dean Trantalis, a longtime LGBT rights activist who served as co-chair of Americans for Equality, said the brief reflects a change in prevailing attitudes.

“The long-held grip on the American psyche is now dripping through the fingers of the right-wing,” he said. “Respect for individual freedom has always been an American ideal, Democrat or Republican.”

Trantalis, who in the mid-1990s worked successfully to enact and defend passage of Broward County’s Human Rights Ordinance, which prohibits discrimination based on sexual orientation, and is now a candidate for Fort Lauderdale City Commission, applauded the strategy of “Changing hearts, then changing minds,” and asked, “[Fort Lauderdale] Mayor [Jack] Seiler, are you next?”