On the topic of gerrymandering: For gerrymandering to be a thing, at one point, Democrats had to have been in charge and districts had to have been drawn in their favor. For district boundaries to have changed, Democrats would have to had to have been voted out of those offices.
I think what actually happened is that the composition of voting districts changed to benefit Republicans, and that when they were redrawn, they were redrawn to more accurately reflect their current composition.
The gerrymandering complaint then boils down to a ineffective excuse to try to explain electoral failure. Given the collapse faced by Democrats in most states across the nation in the last eight years, that cannot all be due to gerrymandering. Democrats will have to come to grips with that if they ever wish to dig themselves out of the hole in which they currently find themselves.