“Who was at J.F.K.?”

Brad Lander, a New York City councilman, shouted into the crowd at a community organizing meeting in Brooklyn, where 1,000 people squeezed into a synagogue on a recent weeknight to strategize against President Trump. Outside, activists became bouncers, turning away a line of people from the overstuffed site. Inside, hands shot up in answer and a cheer went up from those who had swarmed the airport to protest Mr. Trump’s executive order banning travel from seven predominantly Muslim countries.

Mr. Lander continued ticking off some of the many other locations where protests have erupted across the city.

“And who was at Foley Square?” The crowd roared again.

“And who was at the protest last week just down the street?” The room almost shook.

The distaste for President Trump in his hometown has convulsed into near daily protests across the city. Summoned by a Facebook post or cellphone alert, New Yorkers have taken to the streets to object to his policies, appointments and executive orders.

All this, however, could merely be a prelude to the moment yet to come — Mr. Trump has still not set foot in New York City as president, puzzling and emboldening some protesters who see his weekend visits to his Florida estate as something of a retreat to friendlier ground. But whenever he does settle into his penthouse home atop Trump Tower, seething New Yorkers will finally be able to train their ire directly at Mr. Trump on his doorstep.

“The visual of Trump coming back to New York would be the Fifth Avenue of Manhattan flooded with people angrily protesting just about everything that Donald Trump has done — I don’t think he wants to create that visual,” said Carl Dix, whose anti-Trump group, Refuse Fascism, has been plastering the city with stickers that say “NO!” “I don’t think he wants the world to see that.”

City officials would not discuss details of security plans that will be used when Mr. Trump returns to the city or how much protecting him will cost. Between his election in November and his inauguration in January, the city spent $37 million for the more than 200 police officers on patrol each day in and around Trump Tower. The federal government has reimbursed the city about $7 million. Large protests would most likely require a bigger police presence.

“Demonstrations do have an impact on operations because we have to get those cops from somewhere,” the police commissioner, James P. O’Neill, told reporters at a news conference in response to questions about how the city would manage Mr. Trump’s return. “Short term, we can handle it, but if it continues to go on, it could have an impact on our operations.”

The White House did not respond to a query about whether or when Mr. Trump would return to his Manhattan home.

Allies of Mr. Trump scoff at the notion that the president is leery of coming back to New York, in part because his wife, Melania, decided to stay here to allow their son, Barron, to finish out the school year.

“Donald Trump will never be chased out of his hometown,” said Roger Stone, a Republican operative who has worked on and off for Mr. Trump for 40 years. Mr. Trump, he added, has long tended to prefer spending winters at his Mar-a-Lago resort in Palm Beach, Fla.

Besides, protests, no matter their size or level of vitriol, may satisfy people who will never embrace Mr. Trump, but do nothing to chip away at his ardent base, Mr. Stone said. “Politically, the demonstrations against you in New York probably help you in flyover country.”

In Mr. Trump’s absence, New York has become something of a proving ground for organized displays of anti-Trump sentiment. From the governor, Andrew M. Cuomo, to the mayor, Bill de Blasio, to an intersectional grass-roots movement that includes Muslims, gays, Latinos and immigrants, among others, New York has been a caldron of unrest.

There have been student walkouts, disruptions at Trump-linked businesses, mass same-sex kiss-ins in front of Trump Tower and Muslim prayer vigils in airport arrival halls. For some the protests have served as beta tests for the main event: Mr. Trump’s homecoming.

“In the event that President Trump does come to New York, we are very much holding him accountable for what he has already done to the immigrant community,” said Thanu Yakupitiyage, a spokeswoman for the New York Immigration Coalition.

Since the election, immigrant groups like the coalition and Make the Road New York have been organizing via text messaging app, blasting participants with calls to action straight to their phones. It helped the coalition attract thousands of people to Kennedy Airport hours after the travel ban went into effect. Events that used to take weeks to launch now take hours, organizers said, foreshadowing what may happen when word filters out that Mr. Trump is on his way.

“Because people are paying attention, we are able to mobilize people with very little notice,” Ms. Yakupitiyage said.

Melissa Byrne, who describes herself as a professional community organizer, helped coordinate a protest a few weeks ago led by the actor Mark Ruffalo outside the Trump International Hotel and Tower in Columbus Circle next to Central Park. Ms. Byrne has been conducting walk-throughs for marches past Trump Tower for other clients. She devises routes with an eye to navigating the tower’s substantial security zone and to avoid the fate of most people who wave signs there: penned behind barricades across the street, where photo opportunities and television angles are subpar.

“Good protests always have to think about how they look,” Ms. Byrne said. “It’s all about the meme.”

A spokesman for Mr. de Blasio, who has positioned himself as a national leader of the opposition to Mr. Trump, said it wasn’t the mayor’s place “to dictate to the president where he should and should not spend his time.” Still, the spokesman, Austin Finan, added that “the mayor supports every individual’s right to protest peacefully and make their voice heard.”

After Mr. Trump canceled a recent appearance in Milwaukee, activists claimed it was as a result of planned demonstrations. But the White House said it was because of a scheduling conflict.

Some organizers and leaders of advocacy groups believe something more than just another protest with the usual signs and slogans is needed whenever Mr. Trump returns.

“Another march on the street with signs isn’t going to get anyone to pay attention,” said Mark Milano, an organizer with Rise and Resist, a group dedicated to demonstrating against Mr. Trump that formed after his election. “It has to be something that is going to raise people’s eyebrows.”

In January, members of his group made their way into the Jean-Georges restaurant inside Trump International Hotel and began coughing, feigning dying in the restaurant in response to the president’s plans to do away with the Affordable Care Act.

“We will be looking for his travel plans, and we are keeping all our ears open for when he is coming back,” Mr. Milano said. He added that they were devising creative ways to attract attention, including perhaps another “die-in.”

While he was president-elect, Mr. Trump spent most of his time in New York, yet rarely left his triplex penthouse. When he comes back he may choose again to stay inside and avoid watching whatever unfolds 58 floors below.

That possibility does not discourage organizers like Ms. Byrne, who say they will be out there, no matter what. “He is addicted to Twitter,” she said. “All you have to do is make sure that the events have really good pictures, and people are talking about it. Because he knows.”

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