New York’s highest court on Wednesday dealt national Democrats a major setback in their quest to keep control of the US House, when it struck down the state’s 26 congressional districts because they were illegally distorted in favor of Democrats.

New York is critical for Democrats in the decennial process of redrawing congressional districts. The state’s 26 seats offer the party one of the richest opportunities to use mapmaking power to their advantage. Democrats currently have a 19-8 advantage in the congressional delegation, but drew a map that gives them three additional seats, increasing their advantage to 22-4 (New York is losing a congressional seat because of population loss). It would give the party 85% of the congressional seats in a state Joe Biden won with about 61% of the vote.

Democrats saw that advantage as a necessary effort to counter aggressive Republican efforts to distort district lines to add Republican-friendly seats in places like Florida, Texas, Tennessee and Georgia. “For Democrats, a maximal gerrymander in New York was almost a prerequisite to any chances of holding the House,” said Dave Wasserman, a redistricting expert at the nonpartisan Cook Political Report.

Over the past few months, observers have noted that the redistricting process appeared to be going unexpectedly well for Democrats, who were buoyed by a mix of court rulings striking down Republican gerrymandered districts and anti-gerrymandering reforms. Some predicted that redistricting would end in a “partisan wash” or potentially even a balanced US House.

Now, that looks increasingly unlikely.

“A couple of months ago redistricting looked like a silver lining in an otherwise bleak election cycle for Democrats. Today, it looks like just another Republican bonus,” he said. “Democrats can’t catch a break.”

Overall, Republicans are poised to pick up between four and five in the House this year, according to FiveThirtyEight. Republicans need to flip five Democratic-held seats to take control of the House.

The ruling in New York, which could cost Democrats three seats, comes just after Florida governor Ron DeSantis successfully pushed an aggressively gerrymandered map that adds four additional GOP seats. The Florida map is already being challenged in state court – voting and civic action groups say the Florida plan obviously violates language in the state constitution prohibiting partisan gerrymandering. But Florida Republicans have firm control of the state supreme court, making any legal challenge an uphill battle.

Meanwhile, the New York ruling is one of several redistricting decisions this year that underscore the increasingly important role state courts are playing in policing partisan gerrymandering. Last month, a court in Maryland struck down the state’s congressional map, also as being too gerrymandered in favor of Democrats. State courts in North Carolina, Kansas and Ohio have all struck down congressional districts as too distorted in favor of the GOP (the Ohio court let a revised map stand for 2022 even though voting rights groups said they were still too biased).

Overall, Republicans have been able to get away with gerrymandering far more districts than Democrats have.

“The fact that Maryland and New York were struck down and Florida, Ron DeSantis went into attack mode totally wipes away what Democrats had hoped.”

There still is a little bit of uncertainty about what the partisan breakdown of New York’s congressional delegation will ultimately look like. The court of appeals appointed a special master to draw the districts by mid May and moved the state’s primary from June until August. Democrats may also appeal the ruling to the US supreme court, which has suggested in recent cases that courts cannot make changes to maps when an election is near.

Even though Republicans have gerrymandered districts much more aggressively in recent years, the New York ruling also offered an embarrassing rebuke for Democrats, who have led national efforts to rein in severe partisan gerrymandering. The four justice majority said state Democrats had ignored a 2014 constitutional amendment, approved by voters, that adopted anti-gerrymandering language and put a bipartisan commission in charge of the process. Democrats drew the districts after the bipartisan commission failed to produce a plan.

Chief Judge Janet DiFiore, who wrote the majority opinion for the court of appeals, rejected the idea that lawmakers could essentially come up with their own plan if the commission failed. Doing so, she wrote, would make the commission “nothing more than ‘window dressing’ masquerading as meaningful reform”.