I don't think the bar is as low as "could the government make enough gruel to keep you from starving." And, given the current experience with vaccine distribution, even that is not certain.

Think of all commercial food products that contain potatoes that could no longer be produced for a time. Potatoes are a significant source of cattle feed. Potato starch has many non-food industrial applications.

Perhaps we wouldn't have millions of deaths, but a year without potatoes would be an historic catastrophe that Americans would remember for decades.