If Hillary runs, this clip will destroy her
Hillary Clinton speaking in a different dialect - YouTube
Why?
O'bama speaks in different dialects for a given audience. So did Bush. So did Clinton. Etc. etc. etc.
So do I and so do you. It's a normal part of speech. You use one voice when you're making a speech to your colleagues, another voice talking to your dog, still another with a foreigner. It's how speech works.
Then again you thought Sarah Palin belonged in the White House so this kind of simple observation may be a mystery to you.