I hate that old, tired, left over expression from the 2008. It's really tacky. Sarah's advisors can do better than that.
It’s been around for a bit longer than 2008:
FIRE IN THE BELLY - “an unquenchable thirst for power or glory; the burning drive to win a race or achieve a goal. As a political phrase, the expression is usually used to indicate a Presidential candidates’ desire to win, particularly the willingness to endure the long contest. It first appeared in print in 1882, in an essay by Robert Louis Stevenson, in which he compared historians Thomas Carlyle and Thomas Babington Macaulay.The source of the expression is not known. Perhaps this metaphor for ambition comes from stoking a potbellied stove or from the fiery sensation of heartfelt heartburn.”
~From “Safire’s New Political Dictionary” by William Safire (Random House, New York, 1993). Pages 249-250.