  I study how strategic communication among voters shapes both political
outcomes and parties' advertising strategies in a model of informative campaign
advertising. Two main results are derived. First, echo chambers arise
endogenously. Surprisingly, a small ideological distance between voters is not
sufficient to guarantee that a chamber is created, bias direction plays a
crucial role. Second, when voters' network entails a significant waste of
information, parties tailor their advertising to the opponent's supporters
rather than to their own.
