Not sure if this is it, but it highlights a book by Ed Morrissey (anti-Trumper) who did autopsy of the 2012 election and came up with 10 counties that swung the election in 2012...
Might be him.
I ‘advanced searched’ again with his name and couldn’t find it - aargh.
It was an article posted here and pretty sure I commented - but it was years ago.