Incumbent-Quality Advantage and Counterfactual Electoral Stagnation in the US Senate

This article examines the extent to which electoral selection based on candidate quality alone can account for the pattern of re-election rates in the US Senate. In the absence of officeholder benefits, electoral selection is simulated using observed dropout rates from 1946 to 2010. This provides a benchmark for the re-election rate that would be generated by incumbent quality advantage alone. The simulation delivers a re-election rate that is almost identical to the observed rate prior to 1980, at around 78 per cent. In the later subsample, quality-based selection generates a re-election rate that is seven percentage points lower than observed. The divergence in the re-election rates in the later subsample is consistent with the findings of vote margin studies that indicate rising incumbency advantage due to officeholder benefits. In addition, it is found here that the quality-based selection first-term re-election rate is significantly lower than the observed first-term re-election rate. This result supports sophomore surge vote margin studies of officeholder benefits.