Human Rights Campaign endorses Mark Kirk (R) over Tammy Duckworth (D) for Senate

In January, even before the Iowa Caucus, the Human Rights Campaign, the nation's largest LGBT rights organization, endorsed Hillary Clinton for president. At the time, the Sanders campaign said, "It’s understandable and consistent with the establishment organizations voting for the establishment candidate, but it’s an endorsement that cannot possibly be based on the facts and the record."

Hillary supporters said Sanders just had sour grapes, while Bernie supporters pointed out that when the membership of organizations are allowed to vote on endorsements, Bernie does well, but when the leadership of organizations make the decisions unilaterally, they choose Hillary.
http://www.democraticunderground.com/12511046133

So now, how to explain the Human Rights Campaign's decision to endorse Republican incumbent Sen. Mark Kirk over Democratic challenger Rep. Tammy Duckworth in the Illinois Senate campaign?

As David Nir has noted in Daily Kos:

Kirk's record on gay rights is far weaker than that of his Democratic opponent, Rep. Tammy Duckworth—according to no less an authority than HRC itself. In 2013-14, Kirk earned just a 78 percent score on HRC's report card, and in 2009-10, he managed an atrocious 39 percent. (Kirk has no rating for 2011-12, presumably because he missed many votes while recovering from a stroke.) By contrast, Duckworth, who was first elected to Congress in 2012, notched a perfect 100 percent in 2013-14. In what universe does it make sense for an advocacy group to support the candidate who is unambiguously worse on their key issues?