Parts of lower Manhattan, NYC have been strongly Democratic since the time of Martin Van Buren's Presidency.
you are surprisingly right. I always thought that New York (Manhattan, Brooklyn, Bronx) were all strongly republican until the Great Depression. Take a look at this link:
http://en.wikipedia.org/wiki/70th_Congress. I'm not sure how the numbering system worked back then but i thought low numbers = new york city and high numbers = buffalo. Notice how numbers 2 through 18 were democratic. I'm assuming most of those districts had high jewish and ethnic catholic populations.
However, in the state of New York, if one was to get outside of the city of New York, it was strongly republican. Even FDR lost almost all the counties in his home state all four times. The only reason he won his home state is because of the city of New York.