[MrB]

He knows the destruction of traditional marriage furthers the goals of the left,
but he also knows that he can’t gain or retain power

if he alienates most of the people.

[Siena Dreaming]

He's hoping to gain support of a large swathe of the middle with the upcoming debt deal.

If he goes with the debt deal he's going to lose a large chunk on the left unless he gets more radical with the gay stuff.

I don't think his gambit will work. IMO He will alienate everyone as you said.