But the Chinese negotiators, led by Mr. Liu, President Xi Jinping’s point man on U.S. trade, balked at guaranteeing the purchases for fear that such managed trade could violate the rules of the World Trade Organization and cause friction between China and its other trading partners.
https://www.wsj.com/articles/us-china-confirm-reaching-phase-one-trade-deal-11576234325?mod=hp_lead_pos1
看这意思好像是这样，美国想要中国政府直接下令企业每年买500亿美元的农产品。但是中国认为这样违背市场规律且违反世贸规则。美国农民也不信，因为这个量比贸易战前2倍还多。