This was a mistake, he may be rallying the base, but it makes him look like a flip-flooper to independent voters.
1. And how much did he get punished for looking like a flip-flopper in 2008 by opposing prop 8 and gay marriage simultaneously?
1b. Surely whatever explanation he gives for switching his position on the issue will sound less fake than that? Millions of Americans have changed their mind about the issue over these recent years...
2. Seriously, is the president not allowed to ever change his position on anything, ever, without it "alienating independent voters" or some other kind of substance-less political jargon?
2b. Um... everything has pros and cons. Even if I concede that Obama is tangibly losing votes with independent voters by making this move (a *big* assumption you're making without evidence), he will benefit in other ways during the campaign in terms of volunteer support and fundraising. It's hard to say definitively that one is greater than the other.