U.S. Senator Lisa Murkowski of Alaska publicly backed gay marriage on Wednesday, becoming the third Republican senator to do so as she spoke out ahead of potentially landmark rulings from the Supreme Court on the issue. Murkowski, 56, wrote in an essay posted on her Senate website that her decision was swayed, in part, by meeting a lesbian couple from Anchorage, one of whom was in the National Guard, who had adopted four children. "This first-class Alaskan family still lives a second-class existence," Murkowski said in her essay. Her announcement comes as the U.S. Supreme Court is expected to rule soon on a challenge to California's ban on gay marriage and a separate lawsuit targeting a provision of federal law that denies same-sex couples certain benefits. She joins Republican Senators Rob Portman of Ohio and Mark Kirk of Illinois who earlier this year joined dozens of Democratic senators who support gay marriage. Twelve of the 50 U.S. states and the District of