This article studies gubernatorial midterm slumps in U.S. state legislative elections. We employ a regression discontinuity design, which allows us to rule out the hypothesis that the midterm slump simply reflects a type of “reversion to the mean” generated by simple partisan swings or the withdrawal of gubernatorial coattails or “anticipatory balancing.” Our results show that the party of the governor experiences an average seat-share loss of about 3.5 percentage points. We also find evidence suggesting that a large share of the variation in gubernatorial midterm slumps can be accounted for by (1) crude partisan balancing and (2) referendums on state economic performance, with approximately equal weight given to each.