It's funny, how everyone seems to forget that Bill Clinton used the MAGA phrase in his campaigning... I think even in the announcement of his candidacy.
You can easily find the video on YouTube, and ironically enough I heard the recording of it on NPR many months ago.
My guess is Trump's folks remember.... Just like they remembered libs saying Baltimore had third world conditions and how Obama referred to thugs, before Trump employed the same terms.
Granted, given the Clinton's love for Robert Byrd, maybe they did have racist thoughts behind their use of it.