First, the “tipping-point” congressional seat — i.e., the majority-making 218th bluest and 218th reddest seat in the House — is slightly more Republican-leaning. Under the old lines, the tipping-point seat had a FiveThirtyEight partisan lean of R+2.3; under the new ones, the tipping-point seat will have a FiveThirtyEight partisan lean of R+2.5 (again, assuming Louisiana’s map is reinstated on appeal).

In the short term (i.e., in this year’s midterms), Republicans are also more likely to pick up seats from redistricting. Remember that all the numbers above merely reflect each seat’s underlying partisanship; they don’t account for which party currently holds each seat. And when we do that, we see that more Democratic-held seats have been turned red this redistricting cycle than Republican-held seats have been turned blue. By my calculations, Republicans can expect a net gain of roughly three or four seats this November due to the effects of redistricting alone — not accounting for shifts in voter preference.

Some of the House map’s GOP bias is due to geography (i.e., the Democratic tendency to cluster in cities, plus rural areas’ tendency to vote Republican). But a lot is also due to deliberate decisions by partisan mapmakers — namely, Republican lawmakers drawing congressional maps that advantage their own party. In 2014, a pair of academics created a metric called the efficiency gap, which attempts to quantify this phenomenon by measuring how efficient a map is at converting votes into seats for a given party. And using this measure, we find that seven of the 11 most biased congressional maps in the country were drawn by Republicans, while only one Democratic-drawn map (Illinois’s) provides Democrats with more than 1.2 undeserved seats.