Zohran Mamdani, the young star of the U.S. left, began his first day as New York mayor Thursday, a term expected to see him clash with President Donald Trump.

The 34-year-old Democrat — virtually unknown a year ago — was officially sworn in just past midnight, as New Yorkers rang in the new year.

New York’s first Muslim mayor took the oath of office during a private ceremony at a decommissioned subway stop under City Hall.

Later Thursday, Mamdani is scheduled to take part in a larger ceremonial inauguration, with speeches from left-wing allies Senator Bernie Sanders and Congresswoman Alexandria Ocasio-Cortez.

Around 4,000 ticketed guests are expected to attend the outdoor event at City Hall. Mamdani’s team also organized a block party to allow tens of thousands of people to watch from streetside viewing areas along Broadway.

“This is truly the honor and the privilege of a lifetime,” Mamdani told reporters after taking the official oath in the first minutes of New Year’s Day.

Ambitious Agenda

It remains to be seen if Mamdani, a self-described democratic socialist, can deliver on his ambitious agenda, which includes rent freezes, universal childcare and free public buses.

Once an election is over, “symbolism only goes so far with voters. Results begin to matter a whole lot more,” said New York University lecturer John Kane.

How Trump behaves could be decisive. The Republican, himself a New Yorker, has repeatedly criticized Mamdani, though the pair held surprisingly cordial talks at the White House in November.

Lincoln Mitchell, a political analyst and professor at Columbia University, said the meeting “couldn't have gone better from Mamdani's perspective.” He warned, however, that their relationship could quickly sour.

One potential flashpoint is immigration raids, as Trump expands his crackdown on migrants across the United States. Mamdani has vowed to protect immigrant communities.

Before the November vote, Trump also threatened to slash federal funding for New York if it elected Mamdani, whom he called a “communist lunatic.” The mayor has said he believes Trump is a fascist.

New Occupant of Mayoral Mansion

Mamdani’s private swearing-in to start his four-year term was performed by New York Attorney General Letitia James, who successfully prosecuted Trump for fraud.

In a first for the city, Mamdani used several Korans to take the oath — two from his family and one that belonged to Puerto Rico-born Black writer Arturo Schomburg, The New York Times reported.

The job comes with a change of address as he moves from his rent-controlled apartment in Queens to Gracie Mansion, the official mayor’s residence on Manhattan’s Upper East Side. Some had wondered if he would move given his campaign focus on affordability. Mamdani said he was doing so mainly for security reasons.

Born in Uganda to a family of Indian origin, Mamdani moved to New York at age seven. He enjoyed an elite upbringing and had a relatively brief political career, serving in the New York State Assembly before being elected mayor.

To compensate for his inexperience, he is surrounding himself with seasoned aides recruited from past mayoral administrations and the Biden administration.

Mamdani has also reached out to business leaders, some of whom had predicted a massive exodus of wealthy New Yorkers if he won. Real estate leaders have debunked those claims.

As a defender of Palestinian rights, he will have to reassure the city’s Jewish community — the largest in the U.S. — of his inclusive leadership. Recently, one of his hires resigned after it was revealed she had posted antisemitic tweets years ago.