Partisan gerrymandering is an abuse that Republicans ought to fear will be deployed against them. In 2018 and 2020, they may lose control of many state legislatures just as the time comes for decennial redistricting. The Illinois GOP, of course, is well acquainted with how the Democrats in Springfield have been able to use their map-drawing power to help keep Michael Madigan in charge of the House for all but two of the past 35 years.