In order to carry the state, the GOP candidate must win 55-60% on the Island, 2/3 upstate and garnish at least 1/3 in the boroughs. It's really tough to do. Democrats outnumber Republicans 46-27% here.
Reagan won almost 2/3 of the island, 2/3 upstate and 1/3 of the boroughs and still only won by 8 pts in 84.
But that's putting 1980s political allegiances on modern New York. It's simply not the case that Republicans
can win 55-60% on Long Island any more, or 1/3 anywhere in NYC outside of Staten Island (where 55-60% would not be unrealistic in a strong showing). Some of that might just reflect that Republicans can't win in NY any more, but the Republicans' key strategy in NY these days is exploiting the upstate-NYC split and thereby trying to eat into Democratic margins in Buffalo, Syracuse, Albany, etc. I'm not sure that strategy can win, but Long Island is not somewhere the Republicans have strength any more (and it's a very recent collapse).