How Many House Seats Does Partisan Redistricting Control Really Influence?

This study measures how much partisan control of redistricting affects election outcomes. Examining 80 years of state government composition, House races, and moderating institutions like preclearance requirements and commissions, the authors find that unified party control provides benefits to both parties over time.

Data & Methods:

• Collected data on partisan state governments, House election results, and redistricting systems (1940-2020).
• Analyzed temporal trends in the impact of redistricting control for Democrats and Republicans.

Findings: Benefit Magnitude Changes Over Time:

• Both parties gained moderate benefits from control historically.
• Benefits peaked when electoral competition was balanced, weakest during partisan dominance.
• Preclearance under VRA hurt Democrats except in very low-vote-share states.
• Redistricting commissions failed to reduce the benefit for controlling parties.
• The benefit vanished significantly by late 20th century before resurging slightly for Republicans.
• Seat benefits are typically modest (less than 10 seats) in modern times, though enough to flip control historically once.

Why This Matters:

The results demonstrate the evolving political landscape and legal constraints surrounding partisan gerrymandering.