40 Wall Street had not been the tallest building in lower Manhattan in the 1970s, when the Twin Towers were constructed, nor was it the tallest in the area after 2001. In fact, a building just one block to the east of 40 Wall Street is taller by 25 feet, i.e., 70 Pine. 40 Wall Street hasn't been the tallest building in lower Manhattan since the 30s, long before Trump was born, and even then just for about two years.

From the WaPo article linked below:

On 9/11, Trump pointed out he now had the tallest building in Lower Manhattan. He didn’t.

Trump’s odd boast on the day of the attacks wasn’t even accurate.

The Washington Post
By
Philip Bump
National correspondent
September 11, 2018

resident Trump's habit of exaggerating or misrepresenting the effects of New York City's worst terrorist attack on him personally began the afternoon of Sept. 11, 2001.

As our Timothy Bella reported Tuesday, Trump was asked by New Jersey station WWOR to weigh in on the import of the attacks on the World Trade Center only a few hours after planes struck its twin towers. One of the station's reporters asked Trump whether a building he owned — 40 Wall Street, a few blocks from the site of the attacks — had suffered any damage.

"40 Wall Street actually was the second-tallest building in downtown Manhattan,” Trump replied, “and it was actually, before the World Trade Center, was the tallest — and then, when they built the World Trade Center, it became known as the second tallest. And now it’s the tallest."

But it wasn't.

The Council on Tall Buildings and Urban Habitat tracks skyscrapers around the world. As of this moment, Trump's building at 40 Wall Street, called the Trump Building, is the 32nd-tallest building that either stands in New York City or is slated to be built there. Here's how the height of the 66 tallest buildings and planned buildings compares with the height of the two WTC towers.

Many of those buildings aren't in Lower Manhattan, generally defined as below 14th Street. Trump said downtown Manhattan, which is generally considered to be the same area. The tallest building in that lower part of the island is the tallest building in the city — and the Western Hemisphere: One World Trade Center, the building that replaced the twin towers.

That building, of course, wasn't in Lower Manhattan on the day of the attacks. It's a remarkable testament to the recent economic boom in New York City that so few of the 66 tallest buildings included in that first chart were in existence in late 2001. Only 15 of them were, including Trump's building on Wall Street.

Many of the new additions aren't in Lower Manhattan but, instead, in Midtown or on the southern end of Central Park.

Back to the point at hand, though. The question is about the overlap of the two preceding charts. Which buildings are both in Lower Manhattan and existed on the day of the attacks? Only four: The Trump Building, 70 Pine, 28 Liberty and the Woolworth Building, at one time the tallest building in the world.

Of those four buildings, Trump's ranked second in height, by 25 feet, to a building one block to the east.

There was a period during which Trump's was the tallest building in Lower Manhattan, but it wasn't immediately before the construction of the World Trade Center in the 1970s. It was for about two years in the 1930s, well before Trump owned it — or was born.

Obviously, that Trump chose to focus on his building's newly elevated status on the day of the attacks themselves was odd. (One WWOR reporter who was there at the time used the word “stunned” to describe how he felt in the moment to Bella.) But it's hardly unusual Trump should make such a claim, and it's not unusual the claim should be inaccurate.

To that end, 40 Wall Street joins several other Trump exaggerations or falsehoods about the 9/11 attacks, including he “helped a little bit” with cleaning up Ground Zero or he saw Muslims in New Jersey celebrating the towers' destruction. The attacks of Sept. 11 play an outsize role in the American imagination. And, it seems, in Trump's.