We are net exporters of all the major staples. At the very least, we can ratchet down subsidies until we are no longer a net exporter of agricultural products; that level of production is sufficient to handle all our essentials.
> If you rely on importing your food and shipping is disrupted due to war, you're screwed.
The biggest exporters of agricultural products to the United States are Mexico and Canada, which also have plenty of excess capacity. Even in the unlikely scenario that some geopolitical rival manages to shut down trade across the Pacific and the Atlantic, we wouldn't be in a place where we have to worry about our food. If somehow our rival also had the capacity to shut down transit of goods across our land borders, they also have the capacity to shut down domestic transit of goods. I.e., even having self sufficiency based on farms in Iowa wouldn't help feed anyone on the coasts.