The redistricting wars, which since 2010 have worked to the advantage of the Republicans, are about to take a potentially significant turn. The midterm elections, along with efforts in states to reduce partisan redistricting, are likely to make the post-2020 battles more competitive.

The 2010 midterm elections cost Democrats control of the U.S. House, but they also did substantial damage to the party’s strength in the states: Democrats lost hundreds of seats in state legislatures and surrendered their majority of governorships to the Republicans.

Before that election, Democrats had full control — governor, state House and state Senate — in 16 states to the Republicans’ nine, with the remainder divided. After the election, Republicans had full control in 20 states to the Democrats’ 11. Since 2010, the Republican advantage in the states has widened. Today, the GOP has full control in 25 states, while Democrats have full control in just eight, according to the National Conference of State Legislatures.

The process of redrawing district lines to give an advantage to one party over another is called "gerrymandering." Here's how it works. (Daron Taylor/The Washington Post)

After the 2010 elections, Republicans flexed their newly acquired power in the states. In addition to implementing a conservative policy agenda, they worked to cement their power by drawing favorable congressional and legislative districts. Those district boundaries have given the GOP a disproportionate share of House seats, based on the overall popular vote in many states.

Gerrymandering is almost as old as the republic. It has been around since the early 1800s, when Massachusetts Gov. Elbridge Gerry signed a bill that included a state Senate district that was portrayed in the Boston Gazette as a winged animal, with claws, a dragon’s head and a long neck at a right angle to its body. The phrase “Gerry-mander” has been part of the vernacular of politics ever since.

Both parties have played this game. When Democrats held power in the states, they produced gerrymandered maps to their advantage. After the 1980 census, Rep. Phil Burton (D-Calif.) boasted about drawing districts that gave his party an outsize advantage. Burton called his convoluted map “my contribution to modern art.” In those days, Republicans sounded like the Democrats of today, lamenting how gerrymandering complicated their efforts to win control of the House.

Women of color candidates see the 2018 midterms as an opportunity to challenge the status quo and break down barriers. (Alice Li, Sarah Hashemi, Kayla Epstein/The Washington Post)

Over the years the courts have dealt with various aspects of redistricting, but until recently they have ducked the contemporary question of what, if anything, constitutes partisan gerrymandering in violation of the Constitution. In its last term, the Supreme Court considered two maps, one from Wisconsin that favored Republicans and another from Maryland that favored Democrats, but declined to make a definitive ruling.

The high court’s reluctance to rule on this question has, for now, thrown the issue of how to produce fairer district lines back into the political process, which makes next month’s midterm elections the first real battle of the post-2020 Census redistricting process. For Democrats, that makes the contests in the states — races for governor and state legislative seats — as important as the federal races that will affect the balance of power in Washington.

One way the redistricting process could be affected is a shift in power in the legislatures. Republicans have been more skillful and determined in this arena in recent years, and Democrats are trying to catch up. Given the normal swings in midterm elections, Democrats should gain a substantial number of legislative seats in November, but the key issue is where those gains take place.

Democratic strategists see opportunities in a handful of states, where closely divided chambers could flip from Republican control to Democratic control if the November political winds are favorable. They include state Senate chambers in Maine, New York, Colorado and Arizona, along with the New Hampshire state House. Democrats have their eye on a couple of other states, but the numbers there are more challenging.

Those changes would not do much to change the balance of power in some of the states with the most gerrymandered maps, such as Wisconsin. In states where Republicans are likely to maintain control of the legislature, a shift in the governorship would change the redistricting process.

The impact of having a governor of one party and a legislature controlled by the other party was made clear in Pennsylvania earlier this year. The state Supreme Court ruled that the existing congressional map constituted partisan gerrymandering in violation of the state constitution and ordered the GOP-controlled legislature to redraw the boundaries. The Supreme Court declined to review the ruling, saying it dealt with the state constitution.

Republicans in the legislature produced another map favorable to their party and Democratic Gov. Tom Wolf vetoed it. Ultimately, the new congressional lines were drawn by a court-appointed expert, and this map is likely to produce gains for the Democrats next month.

Republicans hold 33 governorships to 16 for the Democrats (along with one independent). But this fall, they are playing defense. The Cook Political Report lists 12 Republican-held governorships as toss-ups or worse, compared with just one held by the Democrats. Among the states where Democrats are competitive are several in the industrial Midwest, including Michigan, Wisconsin and Ohio.

Redistricting remains largely in the hands of the politicians, which means it is often an exercise of raw political power. But a third factor is at work that in the long run could have a sizable impact on the goal of producing fairer and more competitive district lines. That is the movement to take redistricting out of the hands of politicians and give it to citizens or other independent bodies.

Not surprisingly, Americans see fair district lines as an essential in U.S. elections. A Pew Research Center study last spring found that 72 percent cited fair and reasonable districts as something they regarded as important. But just 49 percent said they thought that standard was being met at least somewhat well. Not surprisingly, there’s a big partisan split. Republicans were far more likely to say districts are fairly drawn than Democrats, by 63 percent to 39 percent.

A survey by the Bipartisan Policy Center and USA Today conducted in 2013 found that a plurality of Americans (35 percent) favor the use of bipartisan commissions to handle redistricting, followed by the state legislature and governor (28 percent). Citizen commissions or other entities that reduce the influence of politicians have proved successful elsewhere, with California being the most populous state to move in that direction.

Next month, four states will have redistricting commissions on their ballots: Colorado, Michigan, Missouri and Utah. Earlier this year, Ohio voters approved a new redistricting system aimed at producing a more bipartisan process. Wendy Underhill, director of elections and redistricting at the National Conference of State Legislatures, notes that the number of states — five — with votes on redistricting proposals this year equals the number that took votes between 2010 and 2017.

Even if all these initiatives are approved, most states will still rely on politicians for redistricting. But the combination of ballot initiatives and contested elections are likely to make the next round of redistricting more balanced than the last.