An essential component of any democracy is the extent to which citizens can hold legislators accountable via a meaningful threat of electoral defeat. We show that the (precisely calibrated) probability of defeat for an incumbent member of the US House of Representatives has been surprisingly high and nearly constant for at least two thirds of a century. This result coexists with massive and well documented changes in measures of incumbency advantage, electoral margins, ideological polarization, and partisanship. Our interpretation, supported by a new generative statistical model that we validate with extensive out-of-sample tests, is that these are intermediate variables that reflect different states of the partisan battlefield, and lead in interestingly different ways in different periods to the same probability of incumbent loss. Many other challenges to American democracy remain, but this core feature has remained durable.

[This is joint work with Danny Ebanks and Jonathan Katz]