When President Obama’s guests arrive at the White House on Wednesday for a Gay Pride reception — just days after New York became the largest state in the country to make same-sex marriage legal — they will no doubt be in a mood to celebrate. But for their host, who does not endorse same-sex marriage, it could be somewhat awkward. “I think they are trying to share the joy, which is genuine on their part, without changing his position,” Hilary Rosen, a prominent Democratic strategist, said of the White House. “I don’t think he can have it both ways here.”...