In the long-running battle over a proposed 65-story office tower next to Grand Central Terminal, a little-known real estate investor has lobbied New York City officials, supported community opposition and offered to buy the project site from the developer.

Nothing seemed to work.

So as the planned office tower and a rezoning proposed by the de Blasio administration nears the end of the city’s lengthy review, the investor, Andrew S. Penson, brought in a weapon that he hoped would extinguish the project once and for all: Laurence H. Tribe, a liberal constitutional scholar from Harvard.

Mr. Penson owns Grand Central and the unused development rights above it. Mr. Tribe, who taught President Obama when he was a law student, was willing to plunge into the murky world of zoning, air rights and New York real estate.

But as is often the case, a lot of money is at the root of the dispute. For its part, the de Blasio administration is eager to see the project built, if only to signal to the real estate industry that it is not anti-development.