Looking at some of the Michigan county maps here on the Atlas, I've noticed that Nixon beat Kennedy in Genesee County in 1960. I also accessed the Michigan Manual 1961-62 from one of my local academic libraries, and it shows that the Republican candidate for Governor that year, Paul Bagwell, also carried Genesee County. Since Nixon lost both Michigan and the election (even though the latter was one of the closest in our history), because Bagwell lost, and especially because of Democratic strength in Macomb County at that time due to unions, I wonder why that is. Flint is one of the birthplaces of union labor, and if unions were as strong in Genesee County then as they were now, this strikes me as odd, given Macomb County voted heavily for JFK and John B. Swainson (the Democratic candidate for Governor). Did the rural areas of Genesee County simply overpower Flint??? Some theories on this would be nice.
I am guessing rural de-population probably as well as perhaps white flight. Genessee County has a large African-American population and like many manufacturing areas it seems a large chunk of the white population moved elsewhere thus reducing their influence. As for Macomb County, I believe it has a large Catholic community so the fact JFK was Catholic may have had a reason. Also many of those of Southern and Eastern European ancestry voted heavily Democrat until Reagan whereas not so anymore. In many ways the Polish, Italians, French-Canadians, and Irish were like the Latinos today in terms of voting patterns.