All politics are national: Partisan defection in national and subnational elections

Objective: While they were once viewed as largely local or
candidate-centered contests, recent American elections have
come to be dominated by national forces such as presidential
politics and partisanship. Prior research on voter behavior in this
new era of nationalized politics, however, has largely focused on
more high-profile contests and has not examined voter decision
making across multiple levels of government.
Methods: Our study uses cross-sectional (2006–2020) survey
data from the Cooperative Election Study to explore the determinants
of partisan loyalty and defection across both national
and subnational American elections.
Results: We find consistent evidence that citizens increasingly
rely upon national forces—specifically partisan-ideological
sorting and presidential approval—to make decisions about candidates
up and down the ballot.We also find mixed evidence that
evaluations of the national economy inform defection behavior.
Conclusion: These findings indicate that the national political
forces shape voter behavior in national and subnational contests
in effectively identical ways. Thus, the evidence supports
the notion that all (electoral) politics are now national.