It really doesn't have anything to do with this thread - what's in any food may or may not be imported and you should never assume that it's not unless you walked out and saw the combines working - but the US does indeed import wheat and corn. For real. Not just on paper. The futures reports used to end up on my desk for editing; they're not my responsibility anymore (thank goodness) but as of last year it was in the millions of metric tons for wheat. No matter how good the US subsidies are, if we've got bad weather and the good-to-excellent numbers are in the bucket, and Argentina is enjoying a bumper crop, Cargill is going to ship it up from Argentina. Canada we'll buy from even if conditions are great here, because Canada does durum better than we do. The frozen-dough market wants extra gluten and Canada's wheat has it, so we'll pay a premium for it even if our flour is cheaper.
Ugh - memories of HRW and HW and SRW and SW in massive charts and trying to keep the spring varieties straight... grain imports and exports have to be one of the most pernicious topics that exist. However, take my brain pain as proof that we really DO bring in grains to this country.