This very useful analysis explains how the FTVA’s rebuttable presumption of unlawful gerrymandering works and identifies which new congressional maps would trigger that presumption. Unsurprisingly, maps drawn by legislators are much more likely to trigger the presumption than maps drawn by commissions or courts. Also unsurprisingly, both Democratic and Republican legislators draw highly biased maps when they have the opportunity to do so.

We found that states where Republicans control the state legislatures draw congressional maps that disproportionately favor Republican candidates. For instance, in Georgia, North Carolina, Ohio and Texas, Republican candidates are likely to win more seats than if they won seats in proportion to their share of the statewide vote. The Ohio map, for example, makes it likely that Republicans will win two more seats than you would expect, given that in the elections since 2016, 55 percent of voters pulled the lever for Republicans and 45 percent for Democrats.

Indiana, Iowa and Utah, where Republican-controlled legislatures draw the maps, will likely have similar results, with Republican candidates winning one more seat than you would expect from their proportion of the vote. Under the FTVA, if someone brought suit and the federal courts couldn’t assess the map before the state’s 2022 primaries, the courts would have the power to put in place a temporary map or postpone the primary.

Democrats do the same when they draw maps. In blue states such as Maryland, Massachusetts and Oregon, Democratic-controlled legislatures draw maps that are just as likely to tilt districts to their party’s advantage. For instance, Illinois’ map is a mirror image of North Carolina’s, drawn to systematically advantage Democrats — likely giving them about 2.5 more congressional seats than their usual proportion of statewide votes would suggest.

In some states, however, commissions draw the maps. Four states — Arizona, California, Colorado and Michigan — have created commissions that draw districts independently from the legislature. Our analysis finds that the commissions in California, Colorado and Michigan successfully balanced various competing criteria and created the most balanced maps of the cycle so far. The plan in Arizona would trigger the FTVA’s presumption, though the independent commission there might be able to rebut that presumption.