The 2016 presidential contest was awash with charges that the fix was in: Republican Donald Trump repeatedly claimed that the election was rigged against him, while Democrats have accused the Russians of stacking the odds in Trump’s favor.

Less attention was paid to manipulation that occurred not during the presidential race, but before it — in the drawing of lines for hundreds of U.S. and state legislative seats. The result, according to an Associated Press analysis: Republicans had a real advantage.

The AP scrutinized the outcomes of all 435 U.S. House races and about 4,700 state House and Assembly seats up for election last year using a new statistical method of calculating partisan advantage. It’s designed to detect cases in which one party may have won, widened or retained its grip on power through political gerrymandering.