If you don't vote for the Nominee you are a murderer by legal definition.
Watch this
http://www.alternet.org/blogs/video/76665/And then consider this from Wikipedia
http://en.wikipedia.org/wiki/Accessory_(legal_term)
"An accessory is a person who assists in the commission of a crime, but does not actually participate in the commission of the crime as a joint principal. The distinction between an accessory and a principal is a question of fact and degree:
The principal is the one whose acts or omissions, accompanied by the relevant mens rea, are the most immediate cause of the actus reus (Latin for "guilty act").
If two or more people are directly responsible for the actus reus, they can be charged as joint principals (see common purpose). The test to distinguish a joint principal from an accessory is whether the defendant independently contributed to causing the actus reus rather than merely giving generalised and/or limited help and encouragement."
Further-
"In some jurisdictions, an accessory is distinguished from an accomplice, who normally is present at the crime and participates in some way. An accessory must generally have knowledge that a crime is being, or will be committed. A person with such knowledge may become an accessory by helping or encouraging the criminal in some way, or simply by failing to report the crime to proper authority. The assistance to the criminal may be of any type, including emotional or financial assistance as well as physical assistance or concealment."
It goes on to say in summary that in many jurisdictions a knowing accessory is held by definition to be a murderer.
Take whatever "principled" stand you want and cut it however you want but you know what you're vote for McCain is doing.