From Time Magazine:
The amicus brief, organized by former Republican National Committee Chairman Ken Mehlman, was filed for the four same-sex marriage cases the Court will hear on April 28 that could legalize the unions nationwide. In 2013, Mehlman marshaled a similar effort for the case that overturned California’s Proposition 8, which had banned same-sex marriage in the state. Among the signatories are 23 current and former Republicans members of the House of Representatives and Senate and seven current and former Governors. Sens. Susan Collins and Mark Kirk have signed onto the brief, as has Massachusetts Gov. Charlie Baker and former Utah Gov. Jon Huntsman. Other notables include former New York City Mayor Rudy Giuliani, retired Gen. Stanley McChrystal and billionaire GOP mega-donor David Koch. The 2013 brief included 131 signatures, featured many former top aides to Republican presidential nominee Mitt Romney, including his general counsel and two senior advisors. The list has now grown to 303 signatories.
Mehlman, of course, was running the GOP show when 21 states enacted constitutional bans on same-sex marriage. He finally came out in 2010.