For nearly a year, I posted a weekly analysis of the 100 U.S. counties (out of over 3,100 total) which had the highest cumulative rates of COVID-19 cases and deaths per capita. In addition, I also included a running graph which compared the ratio of COVID cases & deaths per capita between blue and red counties to track how this changed over time.
The results were extremely telling: In the early days of the pandemic back in March/April 2020, the blue counties were devastated for a variety of reasons, including heavy population density, the fact they were mostly located along the coasts (usually in cities with major international ports/airport hubs), and so forth. Democrats tend to live in heavily-populated urban areas, while Republicans are prone to live in more sparsely-populated rural areas, so this made sense.
For the first few months, both case and death rates were running as much as 4-5x higher in counties which voted solidly for Hillary Clinton in 2016/Joe Biden in 2020 than in those which voted for Trump in either 2016 or 2020.