By raising questions about McCain's patriotism.
Consider the facts:
McCain by credible accounts was a womanizer; court records show he was an adulterer; he came in 894/899 in his graduating class at Annapolis. This shows he's not a man of high morals and intellectual strength.
But, here's where it gets really interesting: military records show he lost 4 planes (one was not his fault) prior to entering combat; after only 20 hours of combat he gets captured and, by his own account, volunteers to give military secrets in exchange for hospitalization. He goes on to make propaganda for the North Vietnamese and signs a confession to leave Vietnam.
30 years later he led the drive for peace with communist Vietnam, and according to many prominent conservatives, betrayed the MIAs.
Could McCain have been brainwashed and made into an enemy spy? Some say the communists believe that the way to take over a country is to infiltrate. McCain may be their ace in the hole.
http://www.youtube.com/watch?v=dzVxbUOn4EI