It could be if we had the will to do so. History is replete with examples of how China cannot feed their own people. If we stopped sending them food aid mass famine would undoubtedly follow, most likely within half a growing season. China needs the USA WAY more than the USA needs China. And they know it.
Unfortunately they make all the stuff that we buy. 90 percent of medical drugs and medical aids. They need our pork (all their pigs got sick); but we need medicine.