I guess since we don’t know what deal will be made here we can’t really say how effective it would be for just end-consumers to reject items at grocery stores. Judging by the tone (as always with this US administration) it sounds like a deal would include forcing the EU to purchase certain amounts of food. I.e. we would pay for it even though no one actively selects the US brand products in stores

Exactly, this is not the policies of just one (although completely mental) guy. This is republican politics.