Nearly half the states that elect more than one House member have finished adjusting their districts, which is generally done after each 10-year census. While states that hold just over half of the remaining House seats are still at work, one trend is clear: State lawmakers, who in most cases draw the maps, have created more districts where voters skew heavily toward one party, eliminating many districts where voters are more evenly divided in their political preferences.

A Wall Street Journal analysis finds 12 politically competitive districts in the 22 states that have completed their House maps so far, down from 25 such districts currently.

The early figures signal that Republicans are likely to gain the most political power from redistricting. The number of districts with a strong Republican tilt has grown to 77, up from 64 in the current maps, the analysis finds. Districts considered safe terrain for Democratic candidates have grown from 59 to 61.