China on Tuesday took the first step in initiating a legal challenge of the U.S.β tariffs on steel and aluminum at the World Trade Organization, calling into question the validity of U.S. claims that the tariffs were imposed for national security reasons. China said in a previous consultation request under the Safeguards Agreement that the tariffs amounted to safeguard measures βin the name of national security,β while the U.S. contends the tariffs cannot be challenged because they were imposed for...