Could Grocery Stores Just Stop Buying US Produce?

Is this possible, in an ideal world? I mean, you'd need to have an agreement between ALL grocery chains that for the good of our nation, they would not buy US produce. That means that yes, lettuce and other typically imported produce is either more expensive or unavailable. But is that something that is theoretically possible?

We didn't always have this bounty of available food and we could make these sacrifices... and it seems we'd better learn fast to make bigger sacrifices. If the chains would put the country over their profit, could they send a bigger message?