Wow. Our experiment is off to a great start—let's see if we can finish it off sooner than expected.
OK, so what caused Barack Obama to change his mind and actively press for repeal of DADT this year? Offhand, I'd say there are three leading contenders:
Because I'm a milquetoast centrist sellout, I'm going to punt and say that the answer is all three. Obama really has planned to do it all along during his first term but without a more specific timetable; the pressure from gay and lefty advocacy groups helped push congressional leaders into action and they in turn pressured Obama; and there was probably some additional political calculus related to the possibility of Democrats losing their House majority in November. That's my guess, anyway.
1At least, I assume it's apocryphal. I managed to find a reference to it from I.F. Stone in 1969 once, but I've never been able to track it back any further than that.