When the FBI investigated, it traced the emails to Paula Broadwell, bringing to light her affair with Gen Petraeus.

BBC: David Petraeus CIA scandal engulfs US Gen John Allen

When the FBI investigated, it traced the emails to Petraeus biographer Paula Broadwell, bringing to light her affair with the CIA chief.

BBC: General John Allen cleared over 'inappropriate' emails

When the FBI investigated, it traced the emails to Mr Petraeus's biographer Paula Broadwell, bringing to light her affair with the CIA chief.

BBC: White House to nominate Gen John Allen as Nato commander

"It's not negative, its not mean-spirited to be out there and bringing to light the other candidate's record and the other candidate's associations, which are very, very, very troubling for America, " Palin said.

CNN: Palin: Obama put 'ambition above country'