San Francisco Mayor Gavin Newsom used the four-year anniversary of his decision to wed same-sex couples to endorse Assemblyman Mark Leno (D-San Francisco) in his bid for a state Senate seat.

The two Democratic politicians have both weathered criticisms over the years from party leaders for their push to win marriage rights for same-sex couples.

"Here in San Francisco we have benefited tremendously in Mark's public service – first as a supervisor and now as an Assemblyman. I have known Mark for more than 15 years, and there is no question Mark Leno is the best choice for change – that's why I am most pleased to endorse Mark Leno for state Senate," Newsom said in a statement released Wednesday afternoon. "Mark and I have fought side-by-side in the struggle for full civil rights for all."

Termed out of the Assembly this year, Leno is trying to unseat state Senator Carole Migden (D-San Francisco) from her 3rd District seat. The two powerful gay lawmakers will face off against San Francisco Police Commissioner Joseph Alioto Veronese and former state Assemblyman Joe Nation (D-Marin), who officially entered the race last Saturday, in the June 3 primary.

"As my campaign for the state Senate enters the final four months, I am most grateful to have Mayor Newsom's endorsement. Our city has benefited greatly from his executive stewardship, and I look forward to continuing to work with him as a state senator to make San Francisco a better place to live," said Leno.

An aide to Migden did not immediately return a call seeking comment Wednesday.

Newsom was expected to publicly endorse Leno Wednesday night at the Herbst Theatre during a special screening of Pursuit of Equality , the movie directed by his brother-in-law Geoff Callan and Mike Shaw about the city's "Winter of Love" when roughly 4,000 same-sex couples married at City Hall. Migden and her partner, Cris Arguedas, were among the few couples whom the mayor officiated weddings for at the time.

Leno has been the main proponent of a marriage equality bill during his time in the Legislature. On the same day, February 12, 2004, that Newsom stunned the nation by his order to hand out marriage licenses to gay and lesbian couples, Leno introduced his marriage bill into the Assembly.

The mayor's move was a surprise even to Leno, who rushed back from Sacramento to help marry the throngs of couples flocking to City Hall to exchange vows. Instead of bristling at being upstaged by Newsom, Leno leveraged the mayor's decision as a tool to educate his fellow lawmakers on the need to pass pro-gay marriage legislation.

While the bill did pass out of committee that year, it stalled in the Assembly and Leno pulled it for lack of support. But in 2005 he was able to arm-twist enough votes from his fellow lawmakers to see the bill be sent to the desk of Governor Arnold Schwarzenegger.

The governor vetoed the bill, as he did a similar bill last year. The state Supreme Court is set to hear oral arguments in the case stemming from Newsom's stance for marriage equality on March 4.