WASHINGTON — In one of the strongest shows of support for marriage equality ever demonstrated on the political right, more than 80 prominent Republicans have signed on to a Supreme Court brief laying out the conservative case for marriage equality — and elevating the longtime Bush aide behind the effort.

Ken Mehlman, who served as an adviser to President George W. Bush and chairman of the Republican National Committee, has become a leading Republican voice for marriage equality since coming out as a gay man in 2010. But after spending years building the coalition of lawmakers, former governors, and high-level GOP operatives who signed the brief to be filed this week, Mehlman now finds himself at the center of the national marriage debate.

Although the justices won't hear the case until March 26, and eyes are now focused on whether the Obama administration itself will file a brief in support of striking down California's Proposition 8, the Republicans' brief has made waves as a symbol of just how much the landscape has shifted in a few years.

For his part, Mehlman said the case comes down to a simple point of fairness.

"We believe the court should affirm the overturning of Proposition 8 and affirm the fundamental right of every American citizen to marry the person they love," Mehlman told BuzzFeed Tuesday via email. "It impacts such a fundamental right, the right to marry the person you love. What could be more basic and more important to people's happiness, security and freedom? And as the men and women on this brief thought about their own fundamental political and constitutional values, we concluded that the court should overturn proposition 8 and re-affirm the right to marriage for all Americans."

Recruiting the group of conservative signatories for the brief was no easy task, said Mehlman, but the years-long process illustrates a shifting consensus on the issue within the Republican Party.

"[We] discussed it with men and women we had worked with in politics around the country. Some of these conversations began a few years ago in my case, with thoughtful people I know trying to think about this issue and sometimes coming to different conclusions than they had before," he said.

The effort resulted in getting two members of Congress on board — Reps. Ileana Ros-Lehtinen and Richard Hanna — along with several former governors and members of Congress, and dozens of former administration officials, campaign staffers, and political consultants.

"I knew there were a lot of Republicans that are supportive, but there's never really been an opportunity like this to get everyone on the same page," said Kathryn Lehman, a Republican lobbyist working with Freedom to Marry and Log Cabin Republicans.

"If we want to be a strong party, we've got to learn to be inclusive, not exclusive," said Ana Navarro, the National Hispanic co-chair for John McCain's presidential campaign and also a co-signer. "And we have got to learn to co-exist as Republicans, whether you are a believer in traditional marriage as only between a man and a woman or whether you are a supporter of marriage equality."

"I think it's important that we don't get caught on the wrong side of history and on the wrong side of love and commitment," Navarro added.