  Political actors frequently manipulate redistricting plans to gain electoral
advantages, a process commonly known as gerrymandering. To address this
problem, several states have implemented institutional reforms including the
establishment of map-drawing commissions. It is difficult to assess the impact
of such reforms because each state structures bundles of complex rules in
different ways. We propose to model redistricting processes as a sequential
game. The equilibrium solution to the game summarizes multi-step institutional
interactions as a single dimensional score. This score measures the leeway
political actors have over the partisan lean of the final plan. Using a
differences-in-differences design, we demonstrate that reforms reduce partisan
bias and increase competitiveness when they constrain partisan actors. We
perform a counterfactual policy analysis to estimate the partisan effects of
enacting recent institutional reforms nationwide. We find that instituting
redistricting commissions generally reduces the current Republican advantage,
but Michigan-style reforms would yield a much greater pro-Democratic effect
than types of redistricting commissions adopted in Ohio and New York.
