Using Smoot-Hawley to say Trump has authority to do this is misleading, at best, and incredibly ignorant, at worst.
For one, SH involved tariffs passed by the HOUSE, not by the President.
For another, it was such an economic poison pill that a new liberal trade bill was passed in 1934 and effectively nullified SH.
Also, the Federal Trade Act of 1974 does not give the President authority to drop sweeping tariffs, it allows him to create trade deals that Congress can pass quickly.