Earlier today, the Human Rights Campaign, the major LGBT advocacy group in DC, endorsed Republican Susan Collins for re-election.
Even though some of her Republican peers like Lisa Murkowski, Rob Portman, and Mark Kirk have publicly supported gay marriage, Susan Collins has not. She always hedges when asked, saying that marriage is an issue of state law. She even used that cop-out when marriage equality was on the ballot in Maine.
Her Democratic challenger, Shenna Bellows (the former Executive Director of the Maine ACLU), was a leader in the fight for marriage equality in Maine and is far more progressive on such issues than Collins. Collins, moreover, would be voting for Mitch McConnell as Majority Leader, a vote which itself should be disqualifying.
Such behavior isn't new to the HRC. In 2008, the HRC endorsed Susan Collins over Democratic representative Tom Allen, who had a higher rating from the Human Rights Campaign.