Madison Square Garden, near the heart of the city, is one of the most famous venues in the world and capable of seating about 20,000. …. New York - viewed by some as a curious choice for the final week of campaigning - is a solid blue state and will not be decisive in the race for the White House.

It’s because it has enough people in its vicinity that support him and could come to fill a 20k person venue. He needed a big rally, but there’s literally nowhere else he can go to do it.