This paper aims to investigate the possibility that electoral campaigning transmits truthful information in a situation where campaigning has a direct persuasive effect on a subset of the electorate called “naïve voters.” To this end, we construct a multi-sender signaling game in which an incumbent and a challenger decide whether to focus on policy or ability in electoral campaigning, and a media outlet then decides whether to gather news. Voters are divided into sophisticated and naïve voters. We demonstrate that a candidate's strategy regarding their issues of focus (campaign messages) can signal his or her private information. Specifically, negative campaigning against the incumbent's ability signals the incumbent's low ability in all separating equilibria. It is also noteworthy that separating equilibria exist only when sophisticated and naïve voters coexist. This implies that a fraction of naïve voters has a non-monotonic effect on the possibility of transmitting truthful information.