The United Nations is going broke as the U.S. and China withhold payments to the institution in a jostle for control. Washington has failed to pay billions of dollars owed to the international body and exited dozens of its programs and agencies, including the World Health Organization, to combat what President Trump describes as wasteful spending and bad policymaking. The U.S. is more than $4 billion in arrears to the U.N. China has compounded the U.N.’s liquidity crisis by slow-walking its own payments, even as Beijing declares itself the organization’s leading defender and, in a jab at the U.S., the...