Tariffs dropped, retaliation avoided, but quotas implied

The U.S. government announced it has dropped a 10 percent tariff on Canadian aluminum exported to the U.S. hours before Canada was set to impose retaliatory tariffs on manufactured aluminum U.S. imports, including aluminum windows and door components. But the Americans are threatening to re-impose tariffs retroactively should Canadian aluminum exports exceed unilaterally imposed quotas.

CBC report

The quotas established by the U.S. fall well below what Canada normally exports, according to the National Post. 

The U.S.-based Aluminum Association said it welcomes the end of tariffs and supports tariff- and quota-free trade in aluminum products between Canada and the U.S.

Trump has invoked Section 232 of the U.S. Trade Expansion Act to justify the tariffs, which would otherwise be in violation of the USMCA free trade agreement. Section 232 allows the U.S. to restrict trade where import of a product would imperil national security. So somehow importing aluminum from Canada is suddenly posing a threat to U.S. national security.