  We focus on the following natural question: is it possible to influence the
outcome of a voting process through the strategic provision of information to
voters who update their beliefs rationally? We investigate whether it is
computationally tractable to design a signaling scheme maximizing the
probability with which the sender's preferred candidate is elected. We focus on
the model recently introduced by Arieli and Babichenko (2019) (i.e., without
inter-agent externalities), and consider, as explanatory examples, $k$-voting
rule and plurality voting. There is a sharp contrast between the case in which
private signals are allowed and the more restrictive setting in which only
public signals are allowed. In the former, we show that an optimal signaling
scheme can be computed efficiently both under a $k$-voting rule and plurality
voting. In establishing these results, we provide two general (i.e., applicable
to settings beyond voting) contributions. Specifically, we extend a well known
result by Dughmi and Xu (2017) to more general settings, and prove that, when
the sender's utility function is anonymous, computing an optimal signaling
scheme is fixed parameter tractable w.r.t. the number of receivers' actions. In
the public signaling case, we show that the sender's optimal expected return
cannot be approximated to within any factor under a $k$-voting rule. This
negative result easily extends to plurality voting and problems where utility
functions are anonymous.
