“Donors will respond, but they need to be convinced that they’re going to be given a good proposition for what’s done with their money,” he said in January at the World Economic Forum. “The Haiti cholera story is not actually a very good one, in that it’s taken us a rather long time to get on top of it, and still the problem is persisting.”

The fund-raising effort has been further complicated by the Trump administration’s intention to cut spending on foreign aid. The United States, historically a leading source of Haiti’s foreign aid, is also the biggest single financing source for the United Nations, which may now confront painful choices over how to allocate reduced revenue.

Ross Mountain, a veteran United Nations aid official who is its senior adviser on cholera in Haiti, said that a number of ideas concerning the financing were under discussion. And, he said, while “$400 million is not a very large sum, considering the circumstances, we are all very aware about the competing demands.”

Mr. Mountain also conceded that “on the financial side, we have not moved further ahead.”

Mr. Trump’s new United Nations ambassador, Nikki R. Haley, who has called the cholera crisis “nothing short of devastating,” did not respond to requests for comment about the funding problem. But in her Senate confirmation testimony in January, Ms. Haley said, “We’re going to have to make this right with Haiti, without question, and the U.N. is going to have to take responsibility.”

Cholera, a waterborne bacterial scourge that can cause acute diarrhea and fatal dehydration if not treated quickly, has killed nearly 10,000 people and sickened nearly 800,000 in Haiti, the Western Hemisphere’s poorest country, since it was introduced there in 2010 by infected Nepalese members of a United Nations peacekeeping force. This year, as of late February, nearly 2,000 new cases had been reported, amounting to hundreds a week.

Studies have traced the highly contagious disease to sloppy sanitation that had leached fecal waste laced with cholera germs from latrines used by the Nepalese peacekeepers into the water supply.