In the last few months of 2020, I think the Democratic candidate at that final sprint point will probably have to/should probably prioritize these ten states, in order:
1) Florida
2) Pennsylvania
3) Michigan
4) Minnesota
5) Wisconsin
6) Virginia
7) Nevada
Colorado
9) New Hampshire
10) Maine
These calculations are based on how close the states are to 50-50 and how EV-rich they are.
Before and after the critical months, though, I think the Democrats should focus on expanding parts of the map like AZ, GA, NC, TX, OH that I believe still won't quite be ready for Democrats yet.
