How many of his own voters does a maskless, crowded, shoutfest called a Trump rally sicken or even kill?
Trump had large rally in Moon Township, Allegheny County, Pennsylvania on 9/22. I don't have numbers; no news outlet made any estimates. Saw some photos and I'd guess maybe around 5,000 (unless the crowd was photoshopped as the famous Inauguration photos were).
Allegheny County has had fairly low spread since March. We've usually been a "yellow" county; we were briefly "orange" after the bars were opened up more in July, but the spread has decreased some since then when bar hours were restricted again.
Moon Township is in the Western central part of Allegheny County and is home to the Pittsburgh International Airport. It tends to vote red, but just barely. I worked in a Moon county district for 3 elections including 2016. While the red candidates usually won, they never won by much. Amazingly in 2016, both Hillary Clinton and Katie McGinty won by a few votes in that district, but lost at the state level (though not by much). Location of Moon Township:
Here's current COVID19 info from Allegheny county & COVIDACTNOW stats. Will update at least weekly. Had low spread so far. Moon Township has had 92 Coronavirus cases/10,000 & 9 deaths. North Fayette Township has had 69 cases/10,000 & 3 deaths.
Here's a Johns Hopkins University map from 9/24, showing the COVID-19 spread in counties in southwestern Pennsylvania, eastern Ohio, the panhandle of West Virginia and a bit of northwestern Maryland. The one dark-colored county indicating higher COVID-19 spread is Columbiana County in Ohio south of Youngstown. Interestingly, Pence spoke in Columbiana County 3 weeks ago (September 4).