Update, January 23, 2019: On the Facebook page for this link post, Charles Steindel says:

Okay, I see the connection with Hawkins and Humphrey--though in both cases I don't know if they needed the memory of Martin Luther King to prompt them to insist on the employment mandate (I don't recall Coretta King being particularly prominent in the runup to the HH Act, though that might have been the case). Furthermore, the Fed had no specific macroeconomic mandate prior to HH, except, perhaps, that related to the 1946 Employment Act. I don't see, then, how the HH shifted the Fed away from a pure inflation target.