Since 2008, Nassau has been a pretty consistent 53-54% D, 45% R (dropping to 51% when the third party vote was up in 2016). It's pretty much alone among affluent suburban counties where Trump has performed at roughly the same level as Romney.
I would need to look at a precinct map to confirm, but I think part of this is different wealthy areas cancelling each other out. Garden City, while still quite Republican, was much weaker for Trump than Romney. Meanwhile, Trump did considerably better in Lawrence and the Five Towns region in general where there is a large Orthodox population as well as the northern half of Great Neck (heavily Persian) than Romney did.
