I genuinely don't understand why Clinton would even bother attacking Trump over the birther comments. He'll row back on it slightly later like he has on every "pivot", his supporters won't care because they believe him regardless, people who didn't support him because he was a birther probably weren't persuaded by such a terrible statement anyway, the number of gains to be made here is just tiny. I mean think about it: who was considering voting Trump, but was just tipped over the borderline for not doing so because he was a birther, but was then reconvinced of voting Trump by this apparent retraction? That's like five people in the whole USA, tops. Don't focus on it. If anything, throwing the sink at him over this just feeds him again; he gets all the attention, dominates the airwaves, and Clinton can't define herself. This isn't the killer issue y'all want it to be.
Ignore it. Go do something high profile where you talk about your policies. Plz.