Mayor Bill de Blasio won’t let his crusade against the horse carriages die. His proposal to cap the number of horses and limit their use to Central Park collapsed just before City Council was to vote on it, after opposition was expressed by the Teamsters, the union representing the carriage drivers. Yet the mayor vows to keep trying.

The bill was opposed by drivers, parks advocates and other interests, and had little support from the public.

Often characterized as an “animal rights group,” the main organization pushing the ban was NYCLASS, a pet project of wealthy de Blasio donor and real estate executive Steve Nislick. The same mogul was also the main funder, according to Crain’s New York Business, of NYC is Not for Sale, a political action committee that spent more than $1 million to help defeat Christine Quinn, a de Blasio rival for mayor in 2013, when she refused to support the horse carriage ban as speaker of the City Council.

The mayor appears to have vastly overindulged a wealthy donor’s obsession, another example of the way real estate interests control this city, and of de Blasio’s profligate use of political capital.

He needs to gracefully concede defeat on the horse carriage ban, and to curb his undemocratic instinct to waste time on issues the public doesn’t care about.

The mayor tends to persist on matters that look petty at the expense of the larger vision that inspired us to vote for him in the first place. While some of his feuds — with charter schools leader Eva Moskowitz, for instance, or with Uber — may be based in principle, his failure to explain them has left him looking spiteful. And the horse carriage matter is genuinely as trivial as it looks.

Yet he campaigned on big ideas and substantive change, promising to address economic inequality and attend to racial justice issues like police misconduct. He has achieved impressive things — including universal pre-K, paid sick leave and the New York City ID — that improve New Yorkers’ lives. He’s capable of even more. He needs to curb the pettiness and get back to the agenda that got him elected.

Liza Featherstone lives and writes in Clinton Hill, Brooklyn.