NEW YORK — President Trump sidestepped one of the defining issues of this year’s U.N. General Assembly, giving scant attention to climate change, which dominated the first day of the annual gathering of world leaders and sparked a mass protest in Washington and nationwide.

After scheduling one of his administration’s marquee events — a forum on religious freedom — during the U.N. climate summit on Monday, Trump dropped by the climate event for 14 minutes in a surprise visit. He did not speak and left after listening to remarks from Indian Prime Minister Narendra Modi and Angela Merkel, the outgoing German chancellor. 

“I believe in clean air and clean water, very simple,” Trump said later Monday when asked why he decided to ultimately participate. “We have the cleanest air; we have the cleanest water.”

The minimal attention paid by Trump on the climate issue helped encapsulate how often the U.S. president chooses to forge his own path at multilateral gatherings and how his attention can often be diverted to domestic and political matters. 

Trump used his turn before the cameras at a sit-down meeting with the prime minister of Singapore to tout the U.S. economy and compel a discussion of U.S. manufacturing figures from White House economic adviser Larry Kudlow. Answering questions, Trump gave his personal lawyer, Rudolph W. Giuliani, a rave review for a combative appearance on CNN. 

Trump’s first day at the U.N. General Assembly was overshadowed by the burgeoning controversy over the president’s alleged efforts to pressure Ukranian President Volodymyr Zelensky to investigate former vice president Joe Biden, the 2020 Democratic presidential candidate, and his family. Trump denied doing so on Monday. 

Jon B. Alterman, senior Middle East specialist at the Center for Strategic and International Studies, said other leaders have gotten used to Trump’s brand of diplomacy.

“He sometimes veers off topic, and he surprises people with things they didn’t think would come up, and he relates things that were not planned to be part of the meeting. That’s sort of intimidating the first time around. I think by the time you’ve had your third or fourth meeting, you’ve learned to anticipate it, you’re on your toes, you have your own idea of a strategy.”

Trump’s running monologue on everything from North Korea and Iran to Democratic challengers and gun control dominated U.S. headlines Monday, but the emotional center of the day was 16-year-old climate activist Greta Thunberg.

“I shouldn’t be up here,” she told U.N. diplomats. “I should be back in school on the other side of the ocean,” said Thunberg, who was captured giving Trump a cold stare as he breezed into the climate session.

“Yet you all come to us young people for hope. How dare you?”

During the climate summit, leaders from France, Germany, India and other countries made public their commitment to increase renewable energy consumption and curb fossil fuel burning. Conspicuously missing was the United States, which was essentially invisible from the issue on a day dedicated to climate change. 

“Climate is global by definition, and that means American leadership is required,” Sen. Brian Schatz (D-Hawaii) told The Washington Post on Monday. “But [Trump is] ceding leadership to China and Europe by not being at the table, and sometimes, turning the table upside down.”

Trump billed his administration’s event on religious freedom as the first such meeting at the U.N. that was led by a president of the United States. He also announced that he is launching a coalition of businesses that would encourage all religious beliefs to be protected in the workplace. 

“America stands with believers in every country who ask only for the freedom to live according to the faith that is within their own hearts,” Trump said during the event. “As president, protecting religious freedom is one of my highest priorities and always has been.”

In addition to the religious freedom event and his brief visit to the climate summit, Trump shuffled through one-on-one meetings with a half-dozen world leaders. He is scheduled to deliver his annual address at the U.N. on Tuesday morning, and his meeting with Zelensky is sure to be heavily scrutinized in light of reports that he attempted to pressure him in a July 25 phone call.

As he met with Egyptian President Abdel Fatah al-Sissi, Trump dismissed a question about protests against Sissi’s authoritarian regime, saying that the former Army general had imposed welcome order in his country and overcome “turmoil.” Sissi came to power after the ouster of Islamist leader Mohamed Morsi, who had been democratically elected.

Adopting a dismissive tone, Trump told a reporter that no one is immune to protests, “not even your best friend,” former president Barack Obama.

Trump also said he has had to turn away many requests for meetings here and suggested that French President Emmanuel Macron did not make the cut. Macron wants to bend Trump’s ear about Iran and a French proposal to keep the 2015 international nuclear deal afloat with a $15 billion loan to Tehran. 

Trump is not scheduled to meet with Iranian President Hassan Rouhani this week in New York, although he said he would not rule it out. 

And earlier in the day, Trump reiterated his offer to act as mediator between India and Pakistan over the disputed Kashmir region during a meeting with Pakistani Prime Minister Imran Khan.