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The Policy Consequences of Partisan Gerrymandering

New research finds the issue of how legislative districts are drawn, currently being considered by the Supreme Court, is far from academic.
The United States Supreme Court building in Washington, D.C.

The United States Supreme Court building in Washington, D.C.

On Tuesday, the United States Supreme Court heard arguments in a case that is as important as it is wonky. Essentially, the court will determine whether state legislatures can draw legislative districts in such a way that favors candidates from the majority party.

This debate hasn't attracted anywhere near the attention of highly emotional, hot-button issues like immigration or gun control. But new research shows that the manipulation of district boundaries—a process known as gerrymandering—can directly determine how such issues are resolved, at least on the state level.

"Partisan gerrymandering has major consequences not only for who wins elections, but for the political process as a whole," conclude political scientists Devin Caughey of the Massachusetts Institute of Technology, Chris Tausanovitch of the University of California–Los Angeles, and Christopher Warshaw of George Washington University.

Legislative maps drawn to maximize the power of one party "can lead to policy changes that are difficult to reverse," they write in the Election Law Journal.

The researchers' analysis is based on the concept of the efficiency gap. As we reported back in 2015, this figure measures the number of votes that are "wasted" in a given district—that is, how many additional votes the winning candidate received above and beyond what he or she needed.

A candidate who wins by 50.1 percent of the vote has an extremely low efficiency gap; one who wins by two-to-one has a very high one. This discrepancy is often due to demographics—for instance, largely black inner-city neighborhoods tend to be overwhelmingly Democratic—but they can also be manufactured.

A candidate who wins by 50.1 percent of the vote has an extremely low efficiency gap; one who wins by two-to-one has a very high one.

Using sophisticated software, political parties that control the legislatures in certain states—including Wisconsin, which is the case before the Supreme Court—have redrawn districts to maximize the efficiency of their own wins, and the inefficiency of the other party's wins. If you arrange it so that 80 percent of the voters in one district are Democrats, it makes for a lot of wasted votes, and increases the odds that a Republican in a nearby district can win with just over 50 percent of the vote.

Caughey, Tausanovitch, and Warshaw present evidence that the efficiency gap—whether natural or created for partisan purposes—can have a large and lasting impact on both state politics, and the policies that get enacted into law.

"A closer look at Michigan shows what can happen when there are severe mismatches between voters and legislators," the researchers write. "In the 2011–12 session, Michigan advanced an ambitious conservative agenda that included a large spending cut, higher taxes on pensions, and lower taxes on corporations."

They continue:

Perhaps most significantly, in December 2012, Michigan became a right-to-work state, forbidding contracts that require workers to pay union dues. This was a grievous blow for unions in a state that has historically been a stronghold for organized labor. ... All of this occurred despite the fact that in 2010, Democrats received a bare majority of the votes for the Michigan state assembly, 50.4 percent. Despite this performance, Republicans received 57.3 percent of the seats. This allowed Republicans to pass the right-to-work law without a single Democratic vote, and despite a few defections from their own memberships.

The researchers add that the efficiency gap favoring Michigan Republicans, already substantial in 2010, has grown since due to post-census redistricting controlled by the majority party. In both 2012 and 2014, "Democrats received majorities of the state assembly votes, but minorities of the seats," they note.

"Even if the Democrats win back the governorship," they add, "it will be very hard to win back the state assembly given the districts that have been drawn."

Of course, Republicans may be pleased with this scenario. But they need to keep in mind that, although "pro-Republican efficiency gaps have a larger effect on state legislative behavior than pro-Democratic efficiency gaps," the advantage is not always with the GOP.

The researchers note that, thanks to a sizable efficiency gap, Democrats were able to win 51 percent of the seats in the Vermont House of Representatives in 1998. "In the ensuing term, the state house narrowly approved a controversial bill providing for same-sex civil unions, which ultimately became the first such law in the nation," they note.

The Republicans subsequently took back the House, but were unable to get the bill repealed—further evidence that laws passed by even a tiny, temporary majority tend to be difficult to reverse.

Gerrymandering, legal scholars Cliff Sloan and Michael Waldman recently argued in the Washington Post, "represents an unprecedented threat to our democracy." Given these findings, it's impossible to dismiss that as an exaggeration.