Donald Trump’s gotten under his skin.

Mayor Bill de Blasio grew hoarse shouting over the cranked-up crooning of Frank Sinatra tunes playing in the Trump Tower lobby as he tried to promote his “Green New Deal.”

The mayor had planned a press conference outside the tower that houses president’s Manhattan residence, but Mother Nature forced him to relocate the event into some very unfriendly territory—the gilded building’s public lobby.

“Had the weather cooperated we would have been outside,” the mayor admitted.

The atrium is one of several privately-owned, public spaces in the city that are created in exchange for loosening height restrictions.

Trump Tower staff turned up the dial on the PA system just moments before the mayor entered the 5th Avenue building. Tony Bennet’s “Stranger in Paradise” and Frank Sinatra’s “I’ve Got You Under My Skin” blasted through the speakers during the event.

Trump supporters joined in the noise heckling the mayor with a steady stream of “Boos” and “You s—ks” as he tried to shout over the din.

“Worst mayor ever,” read one sign held by a protester as the mayor rode up and down an escalator.

Other supporters loudly booed and whistled as de Blasio tried to shout over the din.

“This is bull—t,” Juliet Germanotta, 37, told The Post as she displayed an “LGBT for Trump” banner behind the mayor’s podium.

De Blasio told his backers and the hecklers, “Clearly the Trump Organization is a little sensitive to the fact that we’re calling them out for what they are doing to the climate but we are not backing down.”

“We will take your money. We will hold you accountable,” de Blasio said, his voice growing hoarse.

The Trump Organization faces the seven-figure penalties if the company doesn’t retrofit eight of its New York City buildings by 2030.

City officials said the properties emit 27,000 tons of greenhouse gases every year — equal to 5,800 cars.

De Blasio asked his boosters to “scream loud enough so they can hear it all the way to the White House, ‘Our planet, not your profit.’ ”

“We will not let you mortgage our future for your real estate,” the mayor vowed.

The lobby is the same location where Donald Trump announced his White House bid in 2015. The press conference was located inside Trump Tower because of the rain.

It wasn’t a hospitable venue for de Blasio, a Democrat who said he will make a decision this month on whether to run for the White House.

Music started playing loudly shortly before the mayor arrived.

The rally was just steps from Trump’s campaign store that sells hats and wine glasses embossed with the president’s name.