Republican-led legislatures’ map changes are estimated to have shifted about eight more seats toward Republicans than Democrats. Whether that advantage holds is up to voters — and the political conditions used to design many of the new districts may already have shifted.

Republicans drew some districts in part around how people voted in the 2024 presidential election. Voters who backed Trump then may choose Democrats or stay home in the midterms, potentially putting some of the districts Republicans targeted back in play.

Mid-decade redistricting is unusual. States typically redraw congressional boundaries early in each decade, after the census. Trump’s call for another round set off a national political struggle, including clashes in Texas, where Republican officials issued arrest warrants for Democratic legislators who left the state, and Louisiana, where the governor suspended a primary after thousands of ballots had been cast so district lines could be redrawn.

In Missouri, the state Supreme Court found the Republican secretary of state in contempt for continuing to use a GOP map that was not legally in effect. Democrats pursued countermeasures in California and Virginia, but Virginia’s plan was later thrown out by the courts. Meanwhile, a U.S. Supreme Court decision weakening the Voting Rights Act prompted rushed redistricting sessions that in many cases reduced minority communities’ voting power.

Not every Republican-led legislature followed Trump’s request. Lawmakers in Indiana and South Carolina rejected redistricting plans. Overall, however, the mid-decade changes amounted to a rare burst of mapmaking not seen at this scale since the 1960s, when courts established the current rules.

The new lines could influence which communities are grouped together and how effectively voters can choose representatives responsive to them. But the estimated partisan advantage is not a guarantee: the November results will show whether the maps’ assumptions match the electorate that turns out.