I think Sept 11 is pretty late in the game....A lot of the money will get off the sidelines by then....I think its too late...IMHO....
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July 4th would have been a perfect ending to her History tour and timed well with the movie etc.....
By announcing later she lets the also-rans duke it out and eliminates them from targeting her. Sound strategery.
The only reasonable thing that would keep her out would be if someone she truly trusts declares. Doubt that this will happen.
BTW, I believe her first choice for a running mate just expressed interest in being VP.
Palin/West 2012