All of their plans would/will cause an economic collapse here. It's one thing that across the political spectrum in economics most agree on. It works well in other countries that haven't fully globalized their economies because they haven't given up the self sufficiency yet. We have. Like you mention most of our food is imported. Food prices would skyrocket if they do flat tariffs across the board. Targeted ones that are slowly rolled out might mitigate the adjustment period, but I'm pretty skeptical of that given the current economic situation here. We can get back to self-sufficient economics but it will not be easy and will wipe out another generation of American workers by giving us the screw. It will also foster increased international tensions, since it is economic interdependence that is largely responsible for the postwar consensus we've been living in.
Plus with Elon saying that things are going to get really hard on the middle class for a while, I think they know full well that they're going to tank the economy. It's another way for them to do a massive wealth transfer from what little the masses still have. The plan has long been to turn us into a fully rent based society where we can't ever own anything. It's the slavery of control through economics rather than force. Much like what the US did to the world after WWII, they're now using that strategy on us.