In the summer of 2021, Black and working-class New York Democrats exhausted by the pandemic and increasingly worried about crime embraced Eric Adams, a former police captain who made public safety the centerpiece of his mayoral primary campaign.

By that fall, a broader swath of New Yorkers — including the more affluent and educated Manhattanites who had been skeptical of him in the primary — decided to take a chance on Mr. Adams, with some embracing his up-by-the-bootstraps biographic claims and pledges to combat both crime and police brutality. And as he took office, even many Republicans in the city voiced optimism for his time as mayor.

But it didn’t take long for that sense of good will to erode. And by the time Mr. Adams abandoned his re-election campaign on Sunday, the man who once trumpeted his “historic, diverse, five-borough coalition” was getting trounced in every borough and with every demographic. The multiracial coalition he had once assembled — from East New York to East Tremont — was in tatters.

In that 2021 primary race, results sometimes broke down along geographic lines. Across parts of Crown Heights, for instance, ​​Eastern Parkway marked the divide between the older, working-class voters of color who preferred Mr. Adams, and the young professionals who embraced his chief progressive rival at the time, Maya Wiley.

At the start of Mr. Adams’s term, polling showed that nearly two-thirds of New Yorkers were optimistic about what his time as mayor would bring. That optimism was strong across every borough, racial group and age bracket, and even included nearly half of Republicans. Mr. Adams performed particularly well with older and Black voters, while voters under the age of 35 were somewhat less enthusiastic.

A swirl of scandals and accusations of corruption quickly ended that honeymoon.

“His approval rating capsized early on,” said Lee M. Miringoff, the director of the Marist Institute for Public Opinion. “The coalition that got him in initially dissipated, and there was no real identity to his administration positively.”

Less than two years into his term, Mr. Adams was facing backlash against his handling of the migrant crisis and a federal investigation into his campaign fund-raising.

By December 2023, his approval ratings were dismal — just 28 percent of New Yorkers approved of his job performance, according to a Quinnipiac University poll.

Among Black voters, though, his approval ratings remained relatively high, with nearly half still approving of his job performance and less than 40 percent disapproving.

The following September, he became the first sitting mayor of New York City to be charged with a federal crime, and his standing slipped further, especially as he accelerated his overtures to Mr. Trump.

Just 7 percent of New Yorkers thought there had been no wrongdoing, according to a Times/Siena poll taken a month later. Across his onetime coalition — Black voters, older voters, voters without college degrees — most thought he had done something illegal, and those who thought he had not committed a crime overwhelmingly said he had done something unethical.

In April of this year, Mr. Adams, who once called himself “the face of the new Democratic Party,” said that he would instead run for re-election as an independent. The announcement came a day after the dismissal of a five-count federal corruption indictment against him, following the Trump administration’s decision to abandon the prosecution.

Even as Mr. Adams rolled out modernized trash collection, reversed planned cuts to preschool programs and announced plans to get drug users off the city’s streets, data from Times/Siena polls show that Mr. Adams’s image had not improved since October of last year.

Earlier this month, a Times/Siena poll found Mr. Adams below 10 percent support among likely voters.

“All of that, I think, came to breaking up the coalition piece by piece,” the Rev. Al Sharpton, the longtime New York civil rights leader, said. “It’s for Zohran or Cuomo to try to grab the pieces.”

A majority of Mr. Adams’s supporters favored former Gov. Andrew M. Cuomo over Assemblyman Zohran Mamdani, the dominant front-runner, the Times/Siena poll found. But even if all of Mr. Adams’s supporters gravitated to Mr. Cuomo, he would still lag substantially behind Mr. Mamdani.

“Where he has ended up,” Mr. Miringoff said, is “an afterthought for a lot of voters, and a very, very low approval rating.”