news analysis
Many state delegations are already under single-party control. New maps could tighten the partisan grip while decreasing the importance of general elections.

Aug. 17, 2025, 5:00 a.m. ET
President Trump’s drive to secure Republican advantage in the House through mid-decade redistricting — and Democrats’ move to retaliate with their own efforts to redraw political lines to their advantage — could supercharge the partisan shift in Congress.
Should the efforts succeed, they would amplify the trend of one party gaining a stranglehold on state congressional delegations, intensifying the deep polarization that has helped to paralyze Congress in recent years.
Even before multiple state legislatures, goaded by Mr. Trump, began to consider redrawing their maps, the number of House delegations represented by a single party was at a 60-year high.
Single-party congressional delegations
Number of states whose House and Senate were controlled by one party
Source: Smart Politics
Notes: Data includes states that had a single-party delegation at some point during the Congress term. The years indicate the beginning of each Congress term.
By Lazaro Gamio and Zach Levitt
A sudden new round of redistricting would continue a remarkable shift of one party gaining congressional supremacy in a state through gerrymandering and ideological shifts, leaving the opposition barely represented or shut out entirely. The result would have profound implications for Congress.
“The number has been on the rise basically since 2010, when Republicans roared back after Obama’s victory,” said Eric Ostermeier, a researcher at the Humphrey School of Public Affairs at the University of Minnesota, who tracks the political makeup of congressional delegations. “Red states are getting redder, blue states are getting bluer. All this data points to this getting worse.”
At present, 12 states have all-Republican House delegations while nine have all Democrats, for a total of 21 — the most since 1965, when Southern states were almost monolithically Democratic, according to Mr. Ostermeier’s historical data. In comparison, an average of just 10 states had single-party delegations from 1983 to 1992, with 21 House seats in those states compared with 57 today.
While the Senate would not be affected by redistricting, the single-party phenomenon is even more pronounced there. By Mr. Ostermeier’s count, only four states have split delegations, the fewest since the direct election of senators began in 1914.
As recently as 2011, 19 states were represented by both Republican and Democratic senators. The steady movement toward single-party Senate delegations has been reflected in the increasing partisanship in a chamber that once was defined by its ability to find compromise.
Current proposals to redraw House maps before the midterm elections next year, instigated by the White House to try to offset the potential for Democratic congressional gains, would tighten the grip that parties have on states where they hold the upper hand politically.
In Texas, where Republicans touched off the nationwide battle, party leaders hope to convert at least five seats to ones strongly favoring them, theoretically increasing their already lopsided majority in the delegation to 30 Republicans and eight Democrats. (Democrats held a 17-to-15 edge in 2003.)
California is threatening to respond with a Democratic push that could result in a 48-4 House Democratic delegation. Other states like Florida, Illinois, Indiana, Missouri and New York are considering jumping into the fight and undertaking a process that historically has taken place only after the decennial census.
The new congressional arms race worries lawmakers who fear the consequences for their institution.
“The gerrymandering that has occurred over the decades has created this situation where multiple states have zero representatives from the other party — not because the voters necessarily chose that, but the politicians chose that,” said Representative Mike Lawler, a New York Republican whose seat could be at risk if his state redraws its map to counter his party’s efforts elsewhere. “That obviously is long-term destructive to the institution and to the country.”
Single-party congressional delegations
States whose House and Senate were controlled by one party
Sources: Smart Politics
Notes: Data includes states that had a single-party delegation at some point during the Congress term. The years indicate the beginning of each Congress term.
By Lazaro Gamio and Zach Levitt
Mr. Lawler and others say the explosion in state delegations under the iron grip of one party has several ramifications. More districts that overwhelmingly favor one party would further dilute the importance of general elections, since primaries are likely to be determinative, giving more extreme elements of the parties more influence.
In addition, lawmakers would lack incentives to work with the other party and risk the wrath of primary voters.
“It truly is foolish to have a situation where we are basically trying to eliminate any bipartisanship at all,” Mr. Lawler said.
Consolidating power in the hands of one party also disenfranchises the thousands of constituents from the opposing party if they are mapped out of having a voice.
“One-power rule and extremism doesn’t get the results that look out for all of the residents of Indiana, and it doesn’t take into account the diversification of beliefs and being able to find the results in the best bipartisan way,” said Representative Frank J. Mrvan, an Indiana Democrat. His district could also be on the line if state Republicans move ahead and try to eke out another seat, turning a 7-2 Republican House delegation majority into an 8-1 advantage.
Single-party delegations were relatively common earlier in the 20th century, with Democrats peaking at 23 states after the landslide election of 1936, according to Mr. Ostermeier.
But in recent decades, most states elected representatives from both parties. That had its obvious advantages, as the party in control of the White House regularly shifted, and states could still claim influence there no matter who was in charge.
Split delegations also allowed states to weather the increasingly frequent changes in control of the House and the Senate by having members on both sides of the aisle. Gone are the days when Democrats had a lock on the House majority for four decades.
“You are going to have the pendulum swing of being in the majority and in the minority, and if you work in a bipartisan way, then it benefits your district, and it benefits the state of Indiana,” said Mr. Mrvan, who said he heard constantly from voters that they wanted to see the parties work together. “So this action of wanting to create districts that are strongly one-sided Republican districts by this administration, I believe, is an overreach.”
Split delegations also encourage lawmakers from the same state to at least occasionally work across the aisle on issues of mutual state interest in a sort of forced bipartisanship.
There is no certainty that the redistricting being considered would produce the desired partisan results. Plucking voters from reliably safe districts to make other seats more competitive could end up costing incumbents who are wary of the redistricting push or deliver other unintended consequences.
It was not long ago that very Republican states such as North Dakota and South Dakota had ample Democratic representation or that states with all-Democratic delegations, such as New Hampshire, were routinely split between the parties.
The transformation in the Senate has been particularly notable. Many states used to send a senator from each party to Washington. They often worked well in tandem on behalf of their states, provided voters a voice in both parties and got along better than senators in the same state from the same party. But those votes are now much more closely aligned with a state’s choice for president, leading to a Senate map that lines up with the electoral map.
“Things changed pretty quickly and pretty greatly in the last 15 to 20 years,” Mr. Ostermeier said.
The prospect of accelerating that change alarms Mr. Lawler, who sees the rush to redistrict as a threat to both parties and to Congress itself.
“It is mutually assured destruction,” he said.
Carl Hulse is the chief Washington correspondent for The Times, primarily writing about Congress and national political races and issues. He has nearly four decades of experience reporting in the nation’s capital.
Comments