Steel Industries, Inc., ordered steel from Interlink Metals & Chemicals. The steel was to be delivered from a Russian mill. There were political and other issues in Russia, and the mill was shut down. Interlink did not deliver the steel to Steel Industries, claiming that it was excused from performance because it could not get the steel from the Russian mill. What would Interlink have to establish to show that it was excused from performing under the doctrine of commercial impracticability?