Voter mobilization campaigns face trade-offs in young democracies. In a large-scale experiment implemented in 2013 with the Kenyan Electoral Commission (IEBC), text messages intended to mobilize voters boosted participation but also decreased trust in electoral institutions after the election, a decrease that was stronger in areas that experienced election-related violence, and for individuals on the losing side of the election. The mobilization backfired because the IEBC promised an electronic voting system that failed, resulting in manual voting and tallying delays. Using a simple model, we show signaling high institutional capacity via a mobilization campaign can negatively affect beliefs about the fairness of the election.