He rues the errors of a bumpy year, conceding that despite an army of political advisers, “the mistakes are mine.”

And he conceded that after a long career as an advocate and strategist, the work of leading 8.5 million New Yorkers has proved more complicated than he expected.

“When you actually have to start with the substance,” Bill de Blasio said on Monday, “the world gets a little more interesting.”

Halfway into his four-year term as the city’s first Democratic mayor in a generation, Mr. de Blasio, 54, is adamant that his policies are changing New Yorkers’ lives for the better, citing historically low crime, fewer traffic deaths, and expanded benefits for immigrants and the working class.

But in a wide-ranging discussion of his tenure, the mayor, whose approval ratings have steadily worsened since he took office two years ago, offered this cleareyed assessment on Monday: “I want to do better.”

“It’s pretty obvious that some things worked as we hoped, and other things didn’t,” Mr. de Blasio told reporters gathered at his invitation in City Hall’s sunlit Governor’s Room. “I’m sober about the fact that, you know, you try a lot of things in leadership and you don’t expect every single one of them to work. You just got to keep learning.”

Over all, 52 percent of New Yorkers say the city is on the wrong track, including 62 percent of whites and 51 percent of Hispanics. Black residents are evenly split.

Mr. de Blasio’s support among white residents has descended to a level so dismal that it has challenged a core assumption of his political strategy: that in a diversifying city, moderate white voters had lost much of their electoral influence, and that the mayor’s path to re-election runs through nonwhite communities.

[. . .]

The mayor’s advisers are now making concerted efforts to recapture the support — or, at least, tamp down the opposition — of a group that, aides fear, could rally around a potential challenger in 2017.

Last year, that task proved daunting for the mayor. This year was different.

Mr. de Blasio arrived on time — a few minutes early, even — to the service in Queens, taking a small step toward repairing his reputation for tardiness among attendees still angry about his late appearance a year ago.

[. . .]

Geri Prado, executive director of the Progressive Agenda Committee, said in a statement on Tuesday that the forum had become unnecessary, because inequality had already moved to the center of the campaign conversation.

The committee had circulated invitations to leading Democratic and Republican presidential candidates, asking them to participate in a public event at the University of Iowa on Dec. 6. The deadline for candidates to respond to the invitation was to be Thursday, according to a copy of the invitation.

As of Tuesday, the University of Iowa had not received notification that any candidate had accepted the invitation, Jeneane Beck, a university spokeswoman, said.

[. . .]

The cancellation was met with expressions of relief by some members of Mr. de Blasio’s inner circle, which was deeply divided over whether the mayor should continue pursuing a forum that many had come to view as a folly.