There was an interesting situation in New York. After the 2020 census, they lost a seat in Congress because their population size shrunk proportional to the rest of the country's. If New York had just avoided 2 or 3 of the larger nursing home COVID outbreaks, they'd have kept the seat.
Very roughly, there's a House seat per 750,000 people in the US. They were really close enough that a couple nursing home populations (in the hundreds) made the difference?
That would be Arizona (0.31%), Georgia (0.24%), and Wisconsin (0.63%), with 37 electoral votes collectively. The total margin in all those states combined was only about 42k votes.
If Trump had won all of those instead, there would have been an electoral college tie, which would have resulted in the House deciding on a one-vote-per-state basis. It wouldn't have been pretty.
Biden also won Pennsylvania, with its 20 electoral votes, by 1.16%.
