@ciaraciaretti,
Hardly any politician ever writes his/her own speeches. People in high office, e.g. a president, will have more than one writer on staff. As has already been pointed out by Setanta and others, these are usually not known as ghost writers. A ghost writer writes a book or long article which is then published under the name of a famous person, as though that person had written it.
As for speech writers, if a candidate for high office actually wrote his/her own speech, it would be "vetted" by a whole army of experts on his staff before he actually delivered it. By the time the editing on such a speech was over, it might well have become something entirely different from what the original contained.
The only time Sara Palin ever sounded as though she knew what she was talking about was when she was delivering a speech written for her.
Btw, welcome to A2k, Chiara.