Did you bother to read the article you cited? I did, and MacWilliam's underlying article he cites (yes, that's a circular citation a no-no in academia) within it.
MacWilliams sole justification and claim to Trump supporters being authoritarian, other than him saying the are comes in his first article here:
https://www.politico.com/magazine/story/2016/01/donald-trump-2016-authoritarian-213533
Then in his second, he adds this without underlying explanation or citation:
https://www.politico.com/news/magazine/2020/09/23/trump-america-authoritarianism-420681
The oddity of this is he overlooks Obama's "Pen and a phone" quote and use of executive orders, and now Biden's right from the get-go. That second paragraph amounts to a bunch of unrelated claims without merit or source.
Bottom line here is that Matthew MacWilliams is an academic hack.
On the website Rate My Professors, he gets good marks for likability but is rated a 2.3 by students for academic rigor
https://www.ratemyprofessors.com/ShowRatings.jsp?tid=1866302
His published works are highly anti-Trump and show gross political bias
https://www.amazon.com/Rise-Trump-Americas-Authoritarian-Spring/dp/1943208026
https://www.amazon.com/Fascism-12-Lessons-American-History-ebook/dp/B084M1B6GP
He got his doctorate at Univ Mass in Philosophy in September 2016. So a philosopher is writing political books about those he completely disagrees with from a radical Leftist viewpoint.