He just won a landmark victory in the Supreme Court over President Trump that paved the way for prosecutors to obtain the president’s tax returns. In February, he won a conviction against Harvey Weinstein in perhaps the biggest criminal case to arise from the #MeToo movement.

So why isn’t Cyrus R. Vance Jr., the Manhattan district attorney, a shoo-in for re-election?

Despite his recent successes, Mr. Vance remains politically vulnerable: He is facing a growing list of emboldened challengers, including two civil rights lawyers, an assemblyman and a former federal prosecutor. Mr. Vance has raised only $29,000 for a re-election campaign, according to his disclosure forms.

And some feminists and advocates for sex abuse victims have criticized the handling of sex crime cases by Mr. Vance’s office.

Through it all, Mr. Vance has not even announced whether he will seek a fourth term next year.

Mr. Vance, 66, declined to be interviewed about his political plans. But he has maintained in recent days that he is focused on getting his office through the coronavirus pandemic, cutting down a backlog of cases that had built up in the months the courts slowed down, and — in response to the protests after the police killing of George Floyd in Minneapolis — addressing inequities within the criminal justice system.

“That’s where my attention is,” Mr. Vance told NY1 last week when asked if he intended to seek re-election.

Still, his effort to investigate Mr. Trump is likely to appeal to his base of Democratic supporters in Manhattan. When Mr. Vance tweeted on Thursday that “no one — not even a president — is above the law,” it was liked more than 30,000 times.

“For New Yorkers, there is nothing bigger than the anti-Trump sentiment, and this case is just monumental when it comes to holding Trump accountable,” said George Arzt, a political consultant who advised Mr. Vance on his first campaign for district attorney, in 2010. “It takes a great deal of courage to go after the president.”

Six months ago, Mr. Vance was considered to be in deep political trouble, having been criticized for his handling of cases against the wealthy and well-connected, including the Trump family and Mr. Weinstein.

Mr. Vance’s office had been called into question over its decision to halt an investigation years ago into whether Mr. Trump and his children misled investors in a condominium project. And though Mr. Vance won the conviction against Mr. Weinstein — the Hollywood producer who is now in prison — he had declined to prosecute him five years earlier.

Now Mr. Vance is pursuing one of the biggest targets of his career: the president. The district attorney’s office sought eight years of business and personal tax records in connection with an investigation of the role that Mr. Trump and the Trump Organization played in hush-money payments made in the run-up to the 2016 election.

The office also focused on whether senior executives at the Trump Organization falsely accounted for the reimbursement as a legal expense to cover up the nature of the payment.

Once the office has access to Mr. Trump’s records, the investigation could broaden beyond the falsifying records law to include any potential financial or tax crimes.

In recent weeks, Mr. Vance has also taken on the New York Police Department after a series of videos showed officers assaulting peaceful protesters during demonstrations against police violence and racism in America.

He has dedicated significant resources to aggressively investigate allegations of police misconduct during the protests and has declined to prosecute demonstrators arrested on minor charges.

Last week, Mr. Vance announced that he intended to prosecute Amy Cooper, a white woman who called the police on a Black bird-watcher in Central Park when he asked her to put her dog on a leash. Ms. Cooper claimed that the man was threatening her, and the case resonated throughout the country, sparking a discussion about white people filing false police reports against Black people.

Mr. Vance said his office was “strongly committed to holding perpetrators of this conduct accountable.” The pending criminal charge against Ms. Cooper appeared to be among the first that a white person in the country has faced for wrongfully calling the police to make a complaint about a Black person.

But some detractors have accused Mr. Vance of pandering to liberal voters in the wake of national protests against racism and police brutality.

“Is this just an exercise in trying to gain some kind of public credit?” said Mark Bederow, a criminal defense lawyer in New York and a former Manhattan prosecutor.

In recent years, Mr. Vance had lost the support of many feminists and advocates for sexual assault victims, who have faulted his office’s handling of sex crimes, including a 2015 case against Mr. Weinstein.

Ambra Battilana Gutierrez, a Filipino-Italian model, had accused the producer of groping her breasts and shoving his hand up her skirt. With the help of the police, she recorded Mr. Weinstein apologizing for touching her. Mr. Vance declined to take the case.

The prosecutor also faced harsh criticism for the way his office agreed to a no-jail plea deal for Robert A. Hadden, a prominent gynecologist who had abused his patients. Elected officials and women’s rights advocates staged protests during Mr. Weinstein’s trial, pointing to the Hadden case as an example of another failed prosecution.

“I think that people and women in particular are asking for more vigorous prosecution and that the harm of this kind of violence be taken seriously for the public safety problem that it is,” said Tali Farhadian Weinstein, a former Brooklyn prosecutor who has announced a run for Manhattan district attorney. “People have been demanding accountability.”

Another challenger, Alvin Bragg, a former federal prosecutor, said that on Mr. Vance’s watch, “people with access and privilege in this town were able to evade accountability.”

But he faulted Mr. Vance for taking a hard line on some minor cases in which he might have shown leniency. Mr. Bragg noted a case in 2018 of a homeless woman who was prosecuted for selling a loose cigarette. Prosecuting those cases, he said, “do not make us safer.”

Mr. Vance’s defenders say he has embraced the goals — popular among progressives — of cutting back on the aggressive enforcement of low-level crimes, which has been shown to have unfair impact on Black and Hispanic residents.

He has stopped prosecuting certain low-level offenses, including possession of and smoking marijuana, subway fare evasion and unlicensed vending. He has said that prosecutions in Manhattan have dropped by 58 percent over the past decade.

His supporters have said that Mr. Vance has pursued risky cases. They point to Mr. Weinstein’s recent case, which raised questions about the issue of consent, and the 2011 case of two officers who were acquitted on charges that they raped a drunken woman after helping her into her apartment while on patrol.

“If you take hard cases, you’re going to lose a few,” said Erin Kramer, Mr. Vance’s former senior adviser. “You don’t want someone who shies away from taking the hard cases because they are afraid of losing.”