that assumes that external suppliers were not already at their cheapest price point and that they were not competing with each other already

it also assumes that there are no other alternative markets to sell to or that supplier capacity is equally elastic; the US might be a high margin market to sell to, but if you only have a fixed amount of product to sell then it makes no sense to eat the high cost of a tariff to keep selling a low margin product when you can instead sell your product at a medium margin in europe

building out more supply for a product is often capital intensive if you want to make it at an economically efficient price point in these times; efficiencies of scale are hard to overcome and a rapid shift of economic policies makes anyone uncertain about future investment so it takes a very long time for these supply chains to rebalance, if they ever do