Standing inside the plaza of Trump Tower in front of the very same escalator that President Donald Trump descended before making his White House bid official, Mayor Bill de Blasio gathered with advocates on Monday to rally in support of New York City’s Green New Deal legislation.

The rally was ostensibly to put the city’s landlords—including the Trump organization —on notice that failure to comply with city legislation requiring buildings to drastically slash their carbon emissions could result in heavy fines. City officials estimated that the Trump organization would owe upwards of $2.1 million annually starting in 2030 if it does not retrofit the eight buildings it owns in the city.

“These buildings are a big part of the problem,” de Blasio insisted, his voice straining at times to be heard over protesters. “We’re making it very clear—it doesn’t matter who you are, even the President of the United States has to abide by the law of this city."

While the mayor acknowledged that there are landlords with larger holdings—and therefore likely bigger polluters—the decision to hold the rally at Trump Tower gave the official, taxpayer-funded function the undeniable air of a political event.

Supporters flanked the mayor holding “NYC Green New Deal” posters, occasionally offering chants of “Our planet not your profit!” while pro-Trump protesters lingered around the edges shouting expletives and waving handmade signs that read “Trump 2020” and “Worst Mayor Ever.”

The New York City Green New Deal was passed by the City Council last month and will become city law this Friday. The aim is to make the city carbon neutral by 2050 with an emphasis on forcing all private and public building owners to modernize their infrastructure. Buildings are responsible for nearly 70 percent of all greenhouse gas emissions in the city.

The rally comes as de Blasio continues to mull a possible run for the 2020 Democratic nomination. While deflecting a question about what he brings to a possible campaign as a straight, white male in an increasingly diverse Democratic party, de Blasio did say that he would announce once and for all whether or not he would launch a presidential campaign this week.

As de Blasio readies a possible campaign run, he repeatedly points to progressive policies enacted here in New York City that he argues could be a model for the rest of the country.

He did so again on Monday, offering a preview of his campaign pitch.

“I’ve said repeatedly, whatever I decide, I’m going to spread all over this country the examples of what we’ve done here in New York. The Green New Deal, in New York City, and particularly the building mandate legislation, is the most advanced plan on Earth by any city, to address global warming,” said de Blasio.

He added, “I expect cities all around the world, all around the country, are going to look at this plan and are going to adopt it. Just like we’ve seen cities all over America pick up on our Pre-K plan, or Vision Zero, or our affordable housing plan. We are showing that you can make real, progressive change on the ground here. And this legislation is groundbreaking, not just in terms of the United States of America, but in terms of the world.”

Brigid Bergin is the City Hall and politics reporter for WNYC. You can follow her on Twitter at @brigidbergin.