I don't know about US politics or this Sarah Palin, I do know about behavior, no she isn't responsible, not even in part, politicians aren't responsible for how people act because those people don't agree with them, that way is madness.
It isn't possible for her, or anyone else for that matter, to get inside heads and twiddle little knobs about. The person who pulled the trigger is solely responsible for his own actions, in the same way that we all are. We may be dealing with another issue if the person concerned is mentally unstable, but that can't be attributed to one person, it is rather, a failure in society in general.
Too often do we hear the remarks from terrorists, or kidnappers, or other criminals, or their supporters, 'look what you made me do, you didn't follow my demands and so you have forced me to kill this person, blow up this building...'