Avalid treaty between the united states and a foreign country provides for the elimination of all tariff barriers between the two countries. it authorizes the president of either country to issue a proclamation nullifying any state or local laws in that country that have the effect of impeding imports from the other country. the foreign country uses the metric system of measurement, and thus all goods produced there and exported to the united states are packaged in metric sizes, such as liters and kilograms. a law of a state in the united states requires all goods sold in that state to be packaged in traditional american sizes, such as quarts or pounds. because the state law substantially impedes imports from the foreign country, the president of the united states has issued a proclamation nullifying the state law pursuant to the treaty. is the president's proclamation valid?