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Ahead of the White House's scheduled release of its 2018 budget proposal Thursday, people familiar with the discussions tell Foreign Policy that State Department staffers have been instructed to cut 50 percent or more of U.S. funding to United Nations programs. The proposal would affect peacekeeping efforts across the world, including in Syria and Yemen, as well as campaigns that provide vaccines to children, fight famine, and monitor nuclear weapons programs.

The United States, for example, contributed $1.5 billion to the United Nations' refugee agency's $4 billion budget last year. Trump's proposal would "leave a gaping hole that other big donors would struggle to fill," said U.N. expert Richard Gowan. "Multiply that across other humanitarian agencies, like the World Food Program, and you are basically talking about the breakdown of the international humanitarian system as we know it."

In December, Trump complained on Twitter that "the United Nations has such great potential but right now it is just a club for people to get together, talk, and have a good time. So sad!" He added: "As to the U.N., things will be different after Jan. 20."

The United States is the biggest contributor to the U.N.'s budget, funding 22 percent of the organization's costs, with Japan the next biggest contributor at 9.7 percent. Read more about what specific programs could be hit at Foreign Policy.