The authors empirically characterize the mechanics of trade adjustment during the Argentine crisis using detailed firm-level customs data covering the universe of import transactions made during 1996-2008. Their main findings are as follows: First, the extensive margin defined as the entry and exit of firms or of products (at the country level) plays a small role during the crisis. Second, the sub-extensive margin defined as the churning of inputs within firms plays a sizeable role in aggregate adjustment. This implies that the true increase in input costs exceeds that imputed from conventional price indices. Third, the relative importance of these margins and of overall trade adjustment varies with firm size. Motivated by these facts, we build a model of trade in intermediate inputs with heterogeneous firms, fixed import costs, and round-about production to evaluate the channels through which a collapse in imports affects TFP (total factor productivity) in manufacturing. Measured aggregate productivity in the sector depends on within-firm adjustments to the varieties imported as well as the joint distribution of each firm's technology and the share of imports in its total spending on inputs. We simulate an imported input cost shock and show that these mechanisms can deliver quantitatively significant declines in manufacturing TFP.