Gerrymandering of Congressional districts could only affect the Presidential election results in two small states, Nebraska and Maine.<p>Eliminating the Electoral College and moving to a nationwide popular vote for President would have essentially no effect on the motivation to gerrymander.<p>On the other hand, if all 50 states allowed each Congressional district to choose its own elector (and presumably elected the other two statewide), it would represent a massive shift in favor of the GOP, and gerrymandering would have very little to do with it.  Instead, the concentration of Democratic votes in urban areas would be decisive.