While electoral clientelism has been studied from very different theoretical perspectives and angles, scholars typically emphasize the importance of organized networks and long-term relations for sustaining it. However, electoral clientelism continues to be widespread in many countries despite the absence of organized parties or electoral machines. In order to solve this puzzle, I propose an informational approach that stresses the indirect effects on electoral outcomes that early investments in electoral clientelism have. I argue that clientelism during campaigns is crucial for signaling candidates' electoral viability. Politicians buy the participation of poor voters at campaign events. By turning out large numbers of people at rallies, candidates establish and demonstrate their electoral prospects to the media, donors, activists, and voters. Evidence from Peru supports these expectations.