  The Shapley-Shubik power index is a measure of each voters power in the
passage or failure of a vote. We extend this measure to graphs and consider a
discrete-time process in which voters may change their vote based on the
outcome of the previous vote. We use this model to study how voter influence
can spread through a network. We find conditions under which a vanishingly
small portion of consenting voters can change the votes of the entirety of the
network. For a particular family of graphs, this process can be modelled using
cellular automata. In particular, we find a connection between this process and
the well-studied cellular automata, Rule 90. We use this connection to show
that such processes can exhibit arbitrarily-long periods.
