Why is southern Brooklyn so Republican?
Primarily ultra-Orthodox Jews, who explain all of the very heavily Republican areas. The more moderately Republican areas are a mix of areas that are heavily "ethnic white" third- and fourth-generation American families (with the most Republican of such areas, like Mill Basin and to a lesser extent Dyker Heights, also being quite wealthy - the more marginal ones tend to be more middle class, but are also rapidly becoming heavily Asian (mainly Chinese) American and more Democratic) and some areas with a lot of recent immigrants from Russia (especially Brighton Beach and Manhattan Beach on the eastern half of Coney Island).
Basically nothing in Brooklyn south of Prospect Park (the six-sided blank space near the middle of the borough) is anything like the stereotypical image non-locals have of the borough.
Thanks. That makes sense. I hooked up with a guy in Flatbush-Ditmas Park and when we were walking to his place, I was sorta feeling like I wasn't even in Brooklyn. It was definitely not the image of a bohemian, urbane, trendy area. It was still nice, but very mixed suburban lowscale kind of nice.