Well, Obama has an opportunity to shut Trump up. The day the offer Trump made all Obama had to do is say, "Done" and have his college transcripts pulled up along with a legitimate birth certificate and tell Trump, "Draw up that check." I think by stifling Trump, it would have boosted him in the polls. And on top of that, a worthy charity would have benefited.
But I guess that is asking a LOT for a president or anyone else to do.
The birther movement is long dead even Mitt has distanced himself and called that a low blow.