Approval of his speech does not equal approval of his job. The speech was also given AFTER the Grammy awards.
https://projects.fivethirtyeight.com...ex_cid=rrpromo
His disapproval rate over the period including the date of the Grammy broadcast, are over 52% or over, including Rassmussen.
Based on that, simple logic leads us to the conclusion that Trump supporters are not of the type to be interested in "liberal" Hollywood or the music industry in the first place and then not likely to have watched the Grammys. The number of Trump supporters watching the Grammys would be significantly less than 50% and therefore it's preposterous that 50% of their audience would be offended by Hillary reading from "Fire and Fury".