Scholars of presidential primaries have long posited a dynamic positive feedback loop between fundraising and electoral success. Yet existing work on both directions of this feedback remains inconclusive and is often explicitly cross-sectional, ignoring the dynamic aspect of the hypothesis. Pairing high-frequency FEC data on contributions and expenditures with Iowa Electronic Markets data on perceived probability of victory, we examine the bidirectional feedback between contributions and viability. We find robust, significant positive feedback in both directions. This might suggest multiple equilibria: a candidate initially anointed as the front-runner able to sustain such status solely by the fundraising advantage conferred despite possessing no advantage in quality. However, simulations suggest the feedback loop cannot, * Much of this work was completed while the authors were affiliated with Wesleyan University. Support has been provided in part by the Plukas Prize Fund at Wesleyan University. The authors would like to thank several anonymous reviewers, seminar participants at the University of Arizona, Andrew Busch, Masami Imai, Jungmo Yoon, and especially Clifford Brown Jr. for detailed and helpful comments.