Are politicians manipulating the artifactual, kinesic, proxemic, or chronemic nonverbal channel?
I think it's a mix of kinesics and proxemics. They are using their bodies to express language (the handshake says, "hi, thanks for coming, thanks for your support"), and it also serves to delineate a boundary between the politician and the other person, by clarifying that "you are welcome to come this close, but not closer."
If you can use two in your answer, I'd do that, but if it's a single choice, then I think you've got to go with kinesic.
Hope this helps.
Matt in New York