These state-level elections could change the balance of power in Congress for a decade

In many states, the winners of 2018 races for governor and state legislative seats will wield considerable power: The once-per-decade responsibility to redraw congressional maps.

After the 2020 Census provides an updated account of where people live, it will be up to the states to adjust their districts to fit that new reality. Elections to the U.S. House will operate under the new maps starting in 2022 and for the following 10 years.

In all, 29 governors and more than 800 state legislators who could have a hand in the new maps will be selected in November, according to the National Conference of State Legislatures.

In some states, the process has brought with it gerrymandering — the drawing of districts to advantage or disadvantage one party or race — tilting the makeup of the U.S. House and resulting in years of legal challenges.

How it works in each state

The most common method for mapping out changes vests power in the state legislature, with approval needed from the governor. This year, many of those states are electing at least a portion of their state Senate that will be in place for redistricting.

Some states have commissions intended to remove biased tinkering with the maps. And some sparsely populated states don’t need to draw districts at all.

Michigan Alabama Alaska Arizona Arkansas California Colorado Connecticut D.C. Delaware Florida Georgia Hawaii Idaho Illinois Indiana Iowa Kansas Kentucky Louisiana Maine Maryland Massachusetts Michigan Minnesota Mississippi Missouri Montana Nebraska Nevada New Hampshire New Jersey New Mexico New York North Carolina North Dakota Ohio Oklahoma Oregon Pennsylvania Rhode Island South Carolina South Dakota Tennessee Texas Utah Vermont Virginia Washington West Virginia Wisconsin Wyoming

Congressional seats are adjusted every 10 years to account for where people live. States gain or lose districts if large population shifts are shown in the decennial Census. The map below shows an estimate of how state totals might change after the 2020 Census.

Census estimates that reflect how people have shifted since 2010 show states in the Mid-Atlantic and Midwest losing seats and states in the South and West gaining them.

Boundaries are also adjusted to account for movement within states. (States need to go through this process for state-level legislative districts as well, though they don’t necessarily handle it the same way.)

In the past, politicians have drawn favorable maps that can misrepresent the share of votes for each party in a state. For instance, if a state loses a seat after the next census, members of a strong majority party could combine two districts currently held by the minority party.

Unless the governor is a member of the minority party and has veto power, there’s little that can be done to stop the maps from proceeding, short of going to court.

[How gerrymandering could decide whether your vote counts]

That’s why who controls state government come 2021 could have a big effect on how fair the maps are.

As it stands, Republicans control both houses of the state legislature and the governorship in 26 states, with Democrats in full control in only eight. In the rest, control is split.

Studies have shown that gerrymandering has happened more frequently in Republican states, but Democratic-controlled states are not immune.

Twelve states have been the subject of litigation this year related to the fairness of their maps. Maryland and Wisconsin maps were recently considered by the U.S. Supreme Court. Pennsylvanians will be voting under a new congressional map after the state’s Supreme Court recently redrew the boundaries.

Many of these states have both gubernatorial and legislative races this year that will determine who plays a role in redistricting.

In some states, citizens or lawmakers are trying to change the way they redistrict to make the process less susceptible to partisanship. An Ohio constitutional amendment that raises the level of bipartisanship required to approve a congressional map passed in May. Colorado, Michigan, Missouri and Utah will have reform measures on the ballot in November.

These reforms, if passed, would alter the power of state legislators to draw maps favorable to certain groups.

But if they fail, and in many other states, the 2018 elections will be an important indicator of whether there will be a check on maps that could govern political power across the country for the next 10 years.

Which 2018 elections could affect redistricting

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