She lambasted the Trump International Hotel & Tower, which appeared over her left shoulder as she delivered a 30 minute speech, as "a shrine to greed, division and vanity" and accused Trump of putting his name on every building.
"He demonizes the vulnerable and he punches down. He puts his name in bold on every building," Gillibrand said. "He does all of this because he wants you to believe he is strong. He is not. Our president is a coward."
Though Gillibrand first said that she was exploring a presidential bid in January, the New York speech was her first since formalizing her efforts last week. It seemed an attempt by her campaign to position Gillibrand in the crowded field of Democrats seeking the party's nomination, a field in which she has been looking to define her path.
Gillibrand spoke as the nation awaited news of the report by the special counsel, Robert Mueller, in the Russia investigation. In her speech, she stressed that "nobody in this country, not even the president, is above the law, or immune from accountability."
She said Sunday, "It is not often that I agree with Richard Nixon, but he was right to say that the American people have the right to know whether their president is a crook." While Attorney General William Barr released a summary of principal conclusions on Sunday, hours after Gillibrand's Manhattan speech, she is among the Democrats calling for the full details.
While some Democrats have taken steps to avoid mentioning Trump on the trail, Gillibrand has not done so. And her decision to re-boot her campaign outside of one of Trump's signature policies, showed her willingness to go after Trump directly. Aides to Gillibrand though dismissed the notion that the choice of venue was crafted to provoke a retort from Trump.
While the president and his campaign have not responded to Gillibrand's speech, a handful of Trump supporters were on hand Sunday, carrying Trump 2020 banners and at times piercing through the speech of Gillibrand and others with chants.
"The people of this country deserve a president who is worthy of your bravery, a president who not only sets an example, but follows yours," Gillibrand told the crowd. "Your bravery inspires me every day, and that's why I'm running for president of the United States."
The event, which took over a portion of Central Park West on a chilly Sunday, focused on a theme of bravery. That theme first appeared in the video she released announcing Sunday's rally. She was joined onstage by more than a half-dozen activists, including young people who were brought to the United States illegally as children, survivors of sexual assault, and anti-gun violence advocates.
In the crowd, a woman sold pink, knit hats with cat ears, recalling the Women's March. Gillibrand was introduced by the actor Connie Britton, who lived with Gillibrand when the two studied abroad in Beijing.
"Knowing her as I do all these years, the consistency of her conviction is clear," Britton said of Gillibrand. "She cannot be knocked down, guys. Not in front of Trump plaza, or anywhere else."