Mr. de Blasio may still have the opportunity to recover some of his lost support. He is still widely viewed as an empathetic figure: 62 percent of residents say the mayor cares “a lot” or “some” about their needs, including half of the whites polled.

And more New Yorkers, 59 percent, say that they are optimistic about Mr. de Blasio’s next two years in office than the 33 percent who say they are pessimistic. (Among whites, the numbers are less encouraging: 41 percent say they are optimistic, versus 53 percent who say they are pessimistic.)

Whites in New York are a large and politically diverse constituency that includes Orthodox Jews in Brooklyn, affluent Manhattanites (and increasingly Brooklynites) and residents of the blue-collar redoubts of outer Queens and Staten Island. In the 2013 mayoral race, whites made up 45 percent of the electorate, with 54 percent supporting Mr. de Blasio.

The mayor has no clear challenger in a re-election bid, and despite his standing with whites, Mr. de Blasio has more or less kept intact the coalition that elected him in 2013: He received positive approval ratings from 57 percent of black residents and 54 percent of Hispanic residents, and from 56 percent of self-described liberals.

Still, a year ago, 70 percent of blacks and 60 percent of Hispanics expressed their approval. Now, only the barest majority of Democrats, 51 percent, approve of the mayor’s job performance. That base of support could be sorely tested if Mr. de Blasio remains deeply unpopular with whites.

Image John Friese, 70, a retired electrician in Canarsie, Brooklyn, is a Republican and does not approve of the mayor's performance: "Yeah, nice pictures of him in Italy eating pasta and stuff, while New York is going down the tubes." Credit... Kirsten Luce for The New York Times

“His job approval is down substantially from a year ago, as is the sense that he has made New York safer, or a better place to live,” said Don Levy, director of the Siena College Research Institute.