The other way a partisan gerrymander can backfire is that there’s fewer truly safe seats. So a smaller shift can cause a wave election. Like, to squeeze every drop from a gerrymander, you don’t create 80% GOP, 20% Dem districts; you make several 55% GOP, 45% Dem districts. It doesn’t take as seismic of a shift to flip an aggressively Gerrymandered map.
The other way a partisan gerrymander can backfire is that there’s fewer truly safe seats. So a smaller shift can cause a wave election. Like, to squeeze every drop from a gerrymander, you don’t create 80% GOP, 20% Dem districts; you make several 55% GOP, 45% Dem districts. It doesn’t take as seismic of a shift to flip an aggressively Gerrymandered map.