AP analysis shows Texas and California redistricting efforts could mess with rare partisan balance

As Texas Republicans and California Democrats redraw U.S. House districts to their advantage ahead of next year’s elections, they’re potentially disrupting a rare partisan balance in American politics.

The 220-215 majority that Republicans won over Democrats in last year’s elections almost perfectly aligns with the share of the vote the two parties received in districts across the U.S., according to an Associated Press analysis. Although the overall outcome was close to neutral, the AP’s analysis shows that Democrats and Republicans each benefited from advantages in particular states.

The AP used a mathematical analysis designed to measure how many more U.S. House seats political parties won in each state beyond what would have been expected from the share of the vote they received. The analysis showed a significant political tilt in one-third of the states’ congressional districts, with either Democrats or Republicans winning at least one more seat than expected.

Where do Democrats hold the biggest edge?

In California, Democrats won 43 of the 52 seats last year — about six more seats than would have been expected based on the average share of the vote for U.S. House candidates of each party. That was the biggest gain among all states.

At the urging of Democratic Gov. Gavin Newsom, California lawmakers on Thursday approved a plan to redraw the district lines created by an independent citizens commission after the 2020 census. Their goal is to give Democrats a better shot at winning five additional seats in next year’s elections — countering a similar move in Texas backed by President Donald Trump.

California’s redistricting plan still requires approval in a special election.

The AP’s analysis found that Democrats won about three more seats than expected in Illinois last year and about two more seats each in Washington, Massachusetts and New Jersey.

Where do Republicans hold the largest advantage?

In Texas, districts were drawn after the census by the Republican-led Legislature and approved by GOP Gov. Greg Abbott. Republicans won 25 of the 38 House seats last year — nearly two more seats than would have been expected based on their average share of the vote.

At the prodding of President Donald Trump, the Legislature is drawing new House districts giving Republicans a shot at winning five more seats in the 2026 midterm elections.

Elsewhere, the AP’s analysis found that Republicans won about two-and-a-half seats more than expected last year in both Florida and North Carolina and nearly two extra seats in Wisconsin.

How has partisan advantage changed over time?

The number of states with congressional districts tilted toward one party or another was higher last year than in either of the past two presidential elections. But those state-by-state advantages essentially canceled each other out.

When adding results from all states, the AP’s analysis showed that Democrats nationwide won about one-half seat more than expected last year. Because congressional seats aren’t allotted by fractions, the net result was that each party’s share of House seats essentially aligned with their share of the votes.

“If you look at the actual congressional results, that map looks pretty darn good at the national level,” said Chris Warshaw, a political scientist at Georgetown University who is an expert in analyzing legislative districts for partisan advantage.

That’s a sharp contrast with other recent elections. In 2020, Republicans won about 10 more House seats than expected based on their share of the vote in that year’s election. In 2016, Republicans won about 25 more seats than expected. Both of those elections were held under congressional maps drawn after the 2010 census.

Districts redrawn based on the 2020 census were first used in 2022 and normally would remain in effect until after the 2030 census. But in some states, there is nothing that prevents politicians from redrawing districts in the middle of a decade, as Texas and California are doing.

How does one party gain an edge over another in House districts?

In many states, U.S. House districts are drawn by the state legislature and subject to approval by the governor. If a political party controls both the legislature and governor’s office — or has such a large legislative majority that it can override vetoes — it can effectively draw districts to its advantage. This is referred to as gerrymandering.

The legislative author of Texas’ new congressional districts, Republican state Rep. Todd Hunter, made that point clear during debate: “The underlying goal of this plan is straightforward — improve Republican political performance,” he said.

One common method of gerrymandering is for a majority party to draw maps that pack voters who support the opposing party into a few districts, thus allowing the majority party to win a greater number of surrounding districts. Another tactic is for the majority party to dilute the power of an opposing party’s voters by spreading them so thinly among multiple districts that it’s extremely difficult for their preferred candidates to win.

Political advantages also can develop naturally. When politically like-minded voters live in the same area — such as urban Democrats or rural Republicans — it can create an edge for the parties even if there is no intent to gerrymander districts.

California’s citizen redistricting commission did not use political data when drawing districts yet still ended up with a U.S. House map favoring Democrats.

“Unless you kind of hardwire in some metric of fairness that has to be met by the plan, a process could easily produce a partisan outcome, even if it wasn’t intended to,” said Eric McGhee, senior fellow at the nonpartisan Public Policy Institute of California.

The AP’s analysis of partisan advantage in congressional districts was based on a model developed by McGhee and Nick Stephanopoulos, a law professor at Harvard University.