Food-aid advocates are praising $331 million in U.S. assistance to alleviate hunger in Africa and the Middle East, even as they wonder whether President Donald Trump will make good on plans to cut assistance from the world’s biggest humanitarian donor.

The pledge is part of a $639 million relief package for South Sudan, Nigeria, Somalia and Yemen announced at last week’s G-20 summit, and will shore up U.S. donations to the United Nations World Food Program, the globe’s top hunger-fighting agency.

“We will maintain leadership in humanitarian assistance,” said Rob Jenkins, deputy assistant administrator for the U.S. Agency for International Development’s humanitarian office. “We hope our action will get other donors to rise to the occasion.”

The contribution was welcomed by the WFP, but the agency also warned that Trump’s push to cut foreign aid has created uncertainty over future donations, which have already slowed responses to humanitarian crises. The UN has called the current global situation the worst since the end of World War II. At least 15 million people are at risk of famine in Yemen, South Sudan and Nigeria, according to USAID.

Trump’s proposed budget includes eliminating most U.S. international food aid. The White House has criticized such programs as inefficient. Budget debates in Washington are being watched closely for signs of a pullback, said Chris Kaye, director of government partnerships for the Rome-based WFP. “We’ve been extremely nervous, and continue to be nervous,” he said.

U.S. contributions to food aid this year, not including its latest announcement, totaled $756 million as of July 9. That would put it on pace for a $1.45 billion annual total, under the more than $2 billion it's contributed the past two years. It’s by far the biggest WFP supporter, accounting for 34 percent of WFP pledges last year. So far in 2017, U.S. funding is at 28 percent.

Some WFP donors have been boosting aid, notably Germany, which is set to become the second-biggest donor this year. But donations to the WFP chronically fall short of what the agency asked for—only $2.66 billion has been given this year versus more than $9.3 billion of identified needs, and last year’s requirements of more than $8.8 billion were met with $5.9 billion in aid.

Responses to this year’s food crises, fueled by civil war and drought,  have been complicated by the slow pace of donations, Kaye said. In South Sudan, for example, the agricultural calendar there meant April and May were crucial months, but aid flows in those months were low, he said.

USAID’s Jenkins said U.S. spending decisions haven’t been affected by the change in administration, and that Congress’s late passage of this year’s government spending bill delayed some allocations.

The Trump administration’s cooler attitude toward food aid is affecting other things, such as arguments within the government over when aid is disbursed, said Jeremy Konondyk, a senior fellow for the Center for Global Development in Washington.

“I don’t know that it’s business as usual quite yet,” said Konondyk, who was a USAID director under President Barack Obama. “When you don’t have political leadership it’s harder to get funds released.”

U.S. leadership can’t be easily replaced, said Barnaby Willitts-King, a research fellow at the Overseas Development Institute in London. “It’s definitely worrying,” he said.

“How countries look at aid is very closely related to what their domestic and national interests are,” Willitts-King said. “This is what’s making it really hard for the whole humanitarian donor community to try to figure out. Is there going to be a sudden pattern in U.S. aid which is going to have huge implications, or is it just part of the budget process?”

July 13, 2017, 4:30PM: Updated with WFP data on yearly unmet needs.