Of course changing circumstances require changing tactics, and if the left was making that argument it’d be a different debate. But that’s not the argument they’re making. They’re not saying the Taliban or Al Qaeda have become less “the people who attacked us on 9/11,” which was one of the left’s tropes ad nauseam during the campaign. Instead they’re saying – explicitly – that Afghanistan’s just not that important. Now it’s true that Obama convinced the American people to trust him as Commander in Chief by saying the exact opposite. But the left didn’t really believe him at the time – they know Democrats have to say moderate-sounding things to get elected, and they don’t hold that against them – so what’s the big deal if he flip-flops now?