Covid-19 has disrupted trade flows and economies all over the world. No surprise, then, that it is disrupting hopes for better trade relations between the U.S. and China, too.

The “phase one” Sino-American trade deal based on big-dollar purchase commitments by the Chinese—rather than major changes in Chinese industrial, tariff or currency policies—was always a dubious proposition, even in normal times. Huge increases in Chinese purchases risked simply shifting trade flows around and pushing up prices of U.S. products, rather than creating net new demand for American goods.

Now, the new coronavirus has shown how difficult executing such an ambitious expansion of managed trade will likely be in a world of fragile global logistics networks and fast-moving epidemics.

China was essentially shut for most of February, its domestic transport networks ground to a halt. It is slowly clawing back to normalcy, but Western economies—and global logistics networks—remain in disarray. U.S. food-processing plants are struggling with rising infection counts and labor problems, while crops rot in the fields.

The impact is already painfully evident in first-quarter trade data. Chinese imports of U.S. farm goods—a major element of the trade deal—did rise sharply. But most of the increase appears to have been before the virus hit: U.S. exports of farm goods to China were up 72% from a year earlier in January, according to the USDA, then down 27% in February.