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Inside Trump Tower, at the foot of a set of escalators in the marble-lined lobby, Mayor Bill de Blasio was nearly ready to begin a news conference on Monday, when the first of many signs of trouble could be heard.
Seven minutes before Mr. de Blasio was to speak, the lobby’s sound speakers suddenly sprung to life. It was Tony Bennett. “Because of You.” “Rags to Riches.” And other gems, all delivered at peak volume.
Mr. de Blasio showed up at 12:04 p.m. A group of activists and city workers chanted, “Our planet. Not your profit.” He stood at a lectern bearing a sign that said “NYC Green New Deal.”
Behind him was another set of other signs — “Worst Mayor Ever,” “Failed Mayor” and “Trump 2020” — that a group of seven men and a woman held aloft, riding up and down the escalators in view of the cameras, as they booed and whistled and heckled and catcalled.
The ostensible reason that Mr. de Blasio was in Trump Tower in Midtown Manhattan was to promote a new city law that aims to force building owners — like Mr. Trump, for example — to curb their energy use as a way to reduce greenhouse gas emissions and to combat climate change.
Mr. Trump, of course, denies that climate change is a problem and has taken numerous steps to halt or curb government efforts to confront it. Which makes him a good foil for any one of nearly two dozen Democratic candidates for president.
Mr. de Blasio, for the record, is not yet one of those candidates, despite holding an event that bore all the earmarks of a campaign event. He said on Monday that he had not yet made a decision and will consult with his family at least one more time before he makes his announcement some time this week.
That meant that his event in Trump Tower was technically a news conference, and not a campaign event. Either way, it was a circus.
Even though he had a microphone and a sound system, Mr. de Blasio had to shout to be heard over the music of Mr. Bennett and the hecklers. After a few minutes, he was hoarse and he could barely get out the ritual “few words in Spanish” with which he invariably ends his public statements.
“Clearly the Trump Organization is a little sensitive to the fact that we are calling them out for what they are doing to the climate,” Mr. de Blasio shouted over the din. He pointed at a poster that said that if Trump Tower does not reduce emissions from current levels by 2030, it would be fined $469,848 under the new law at that time.
The poster included several other properties in New York with Mr. Trump’s name on them, and prospective fines. In fact, most of the buildings, including Trump Tower, are condominiums, which means that the condominium owners (which in some cases include Mr. Trump and his company for portions of the space) would be on the hook for the fines.
“We have a message for President Trump and all the other big building owners in New York City,” Mr. de Blasio said. “Cut your emissions or we will cut something you really care about: We will take your money.”
When it came time for reporters to ask questions, they had to approach the podium and shout as the mayor leaned over with a hand behind his ear in order to hear them.
Why shouldn’t this be seen as a thinly disguised campaign rally?
“This is about a bill that was passed by the City Council,” the mayor replied.
What did he think about the protesters?
“They’re just music to my ears,” the mayor said, “because it means we’re doing something important.”
The event did not escape the attention or criticism of Eric Trump, an executive vice president of the Trump Organization, who said on Twitter that the mayor’s choice of venue was “childish.”
“Most mayors do all they can to support great businesses,” Eric Trump wrote in another Twitter post. “Here in N.Y.C., businesses are attacked for headlines and ‘political points,’” he wrote, adding it is “this very mentality that is causing people to leave our great city in droves.”
Mr. de Blasio has been trying to make the case that his policies in New York City — such as the building emissions law and his expansion of early childhood education — will play well across the country should he run for president.
But the news conference also showed how the mayor’s interest in running for higher office may derive, at least in part, from a desire to escape the persistent interest of local media in probing the minutiae of his mayoral management.
The mayor was asked about an ethics panel inquiry last year into his fund-raising practices, which he has repeatedly refused to acknowledge. He ducked the question again.
And he was asked, for the second week in a row, about a 2015 fender bender involving his official vehicle, which went unreported at the time. An article in The Daily News on Monday said that the mayor’s S.U.V. had crossed over into the opposite flow of traffic on 135th Street at the time of the crash.
Mr. de Blasio ducked again, saying that he was waiting for the Police Department to tell him if the incident was handled properly. (A copy of the police report included the preliminary finding that the mayor’s police driver was “at fault for driving counter flo.”)
Finally the mayor finished and left through the back of the building. His protesters took the equivalent of a victory lap, up and down the escalators (though in fairness it was a draw), and then marched out of the building’s Fifth Avenue doors, exiting under a huge American flag that hangs there. They refused to speak to reporters.
A short time later one of the protesters returned. Wearing a Yankees cap, a brown jacket and jeans, he descended to the lobby’s lower level where he was spotted by one of the building’s security guards. They greeted each other with a handshake and a grin.
“Was that you doing that stuff?” the security guard said. He wore a dark suit.
“Yeah,” the man in the Yankees cap said. He laughed and went to order a sandwich at the Trump Tower cafe, where he was treated like a regular. When a reporter approached and asked him questions he put earbuds in his ears.
Up at street level, someone turned down the volume on Tony Bennett.