I'm not so sure that O'Reilly can be taken that literally here. New York City is quite similar to, but not exactly like, what O'Reilly paints his facetious picture of it being. There is no such thing as irreversible political, social, and economic damage anywhere in the world. New York City has gone Republican in recent times; remember Mayor Rudy Giuliani, for instance?I remember watching this a while back, which ties into why the liberals stay liberals.
I'm certain that in a virtually honest and fair election, free from voter fraud for the most part, Trump would have made a lot more than just 18% in New York City alone. And there might be a good chance that the current Democratic mayor of New York City, Bill de Blasio, could be defeated in his bid for reelection. There are no guarantees, though, but the mayoral election of 2013 had a very low voter turnout if I'm not mistaken.