UPDATE: From Maureen Dowd of The New York Times:
The real danger to the McCain crew in overusing the P.O.W. line so much that it’s a punch line is that it will give Obama an opening for critical questions:
While McCain’s experience was heroic, did it create a worldview incapable of anticipating the limits to U.S. military power in Iraq? Did he fail to absorb the lessons of Vietnam, so that he is doomed to always want to refight it? Did his captivity inform a search-and-destroy, shoot-first-ask-questions-later, “We are all Georgians,” mentality?
(Hat tip to AMERICAblog.)