The simple explanation is that many (but not all) exporters simply stopped exporting things in April (as those shipments would have arrived in May, after the ta

The simple explanation is that many (but not all) exporters simply stopped exporting things in April (as those shipments would have arrived in May, after the tariffs took effect). And many of the factories overseas have cut back on production, especially of low-value goods most affected by tariffs. Smaller ports like Seattle generally handle the overflow from the bigger ports, so they're the first to be affected by the reduction in cargo traffic. Even if tariffs are reduced/eliminated, there will still be a lag of 3-6 weeks before destination-port cargo traffic picks up again, assuming that there is product overseas ready to be shipped.