What is gerrymandering? How a centuries-old political tactic sparked a redistricting firestorm in Texas.

Republicans are threatening to remove Democrats from office or even have them arrested. Democrats have declared “we are at war” and pledged to go “nuclear” in response.

All of this over maps.

How can something so seemingly basic spark such intense rhetoric? That’s because, thanks to a process known as gerrymandering, political fights over maps can become high-stakes contests over power, how it’s wielded and how far the parties are willing to go to protect it.

The current standoff over gerrymandering centers around Texas, where the state’s Republican majority is hoping to approve new maps that redraw the congressional districts to secure their party up to five additional seats in Congress if the maps are in place by next year’s midterm elections. Dozens of Democratic legislators have fled the state to prevent the legislature from considering the maps. So far the tactic has worked, but it’s unclear how long they can hold out or what authority Republicans have to overcome their holdout.

What is gerrymandering?

Every 10 years, the Census determines how the 435 seats in the House of Representatives are divided among the states. That decision is made at the federal level, but it’s the states themselves that choose how to carve up their territory into their allotted number of districts.

In most cases, district maps are approved by the state legislature, which creates an obvious incentive for the party in power to manipulate the maps to their advantage. That’s what gerrymandering is: the process of drawing maps in a way that concentrates one party’s power while diluting the power of the opposition.

Gerrymandering is nothing new. In fact, it has been around longer than either of today’s major political parties. The term was coined all the way back in 1812 after Massachusetts Gov. Elbridge Gerry approved congressional maps that included a winding district that critics said looked like a mythical salamander. Gerry plus salamander became gerrymander, even though Gerry himself found the map to be “highly disagreeable.”

Click the arrows to cycle through different gerrymandering scenarios to see how it works in practice.

How does gerrymandering work?

Voters for the two parties aren’t spread out evenly across the states. They tend to cluster together with others who hold similar political views. Democratic voters are concentrated in big cities, while Republicans usually dominate rural areas. This creates the opportunity for lawmakers to draw lines that tactically distribute their voter base across districts so they can win as many seats as possible.

There are two primary techniques that are used in gerrymandering: cracking and packing. Cracking splits a dense area of one party’s voters into small pieces that are spread out across several districts where they are outnumbered by their political opposition. In Utah, for example, the lines are drawn so the state’s lone Democratic stronghold of Salt Lake City is cracked into four pieces that are each part of larger, mostly rural districts.

The other gerrymandering strategy is called packing, which is when maps cram as many of one party’s voters as possible into a small number of districts so seats elsewhere in the state are safe.

Is gerrymandering legal?

Yes, but with some important caveats. The Supreme Court has ruled that there is nothing in the Constitution barring legislators from designing their state’s districts to give themselves a partisan advantage. Gerrymanders based on race — maps designed to weaken the voting power of a specific minority group — are unconstitutional, however. The distinction between the two types of gerrymandering can be fuzzy because minorities, particularly Black voters, tend to vote for Democrats. In those cases, the court has found that a gerrymander can still be constitutional as long as it was created with a clear intent to dilute minority votes.

Other than the rules against racial gerrymandering, which could change as soon as the next Supreme Court term, the only other nationwide mandate for congressional map drawing is that districts must have roughly the same population. Many states also set additional guidelines for their maps, including the principle that districts should be as geographically compact as possible and that all parts of a district have to be connected.

How did gerrymandering become such a big deal?

There have been complaints about gerrymandering for centuries, but nothing in the past compares with the intensity of the fight over district lines over the past decade and a half.

Things began to escalate after the 2010 Census, when Republicans across the country mounted a coordinated effort to use redistricting to increase GOP control over both state and federal legislatures. The campaign utilized sophisticated mapping technology that had not been available during previous redistricting cycles. The new maps were credited with helping Republicans maintain a strong majority in the House of Representatives in 2012 despite receiving 1.4 million fewer votes than Democrats in House races nationwide.

Republicans kept control of the House during the next two election cycles, in part because of partisan maps that helped them secure more than a dozen seats than they would have otherwise won, according to analysis by the Brennan Center for Justice. Though Democrats were largely caught off guard in 2012, blue states passed their own gerrymanders following the 2020 Census. As a result, the GOP’s districting advantage had been largely erased by the 2022 midterms, according to the Associated Press.

Even in the context of recent gerrymandering, Analysts say the scope and timing of Texas Republicans’ redistricting effort stands out. States usually redraw their districts every 10 years, after the new census determines where House districts will be apportioned. The Texas GOP has opted to create new maps just five years after the state’s last round of redistricting, with the goal of having them in place ahead of the midterms.

Republicans currently control 25 of Texas’s 38 congressional districts. The new map would put them in position to hold 30 House seats after next year, which would give them 80% of the state’s representation in Congress in a state where President Trump secured 56% of the vote in last year’s presidential race, according to the official tally from the Texas Secretary of State. That plan is on hold, however, until the standoff with Democrats who have fled the state is resolved.

Democratic governors in California, New York and Illinois have pledged to gerrymander their own states if the new Texas map does go into effect, but experts say they would face serious hurdles if they do try to go tit-for-tat with the GOP on redistricting.

The outcome of the current redistricting fight could have a huge impact on President Trump’s final two years in the White House. Democrats need to flip only a handful of seats to gain a majority in the House, which would give them veto power over any legislation Trump wanted to pass and the authority to launch high-profile investigations into his actions in office. If Republicans keep control, Trump would enjoy two more years of a Congress that is steadfastly aligned behind his vision for the country.