The US contributes almost 15% of the global wheat exports and 60% of US soybeans go to China. I'm not saying it will end the world but I can't see how it won't have an impact.
One of those stats is not like the other, but regardless, 15% is the sort of impact that rises prices, increasing the search for alternatives, rather than leading to “mass starvation”.
This said, anything that turns Americans angrier is a security risk for the rest of the world.