I came across this while browsing another website. I have not seen it discussed here on CC. The AAU last October voted to expel McGill University and the University of Toronto. Both have been members since 1926. After protests from those institutions and many American institutions the new policy was reversed. Many saw this as an attempt to isolate the top American universities from anything international, figuratively building a northern academic wall between the US and Canada.
https://www.insidehighered.com/blogs/world-view/trend-academic-isolationism-united-states
https://www.insidehighered.com/news/2019/10/08/american-research-university-association-proposes-then-abandons-plan-expel-canadian
https://www.insidehighered.com/sites/default/server_files/media/AAU%20Membership%20Policy%20-%20October%203%202019.pdf
https://www.insidehighered.com/sites/default/server_files/media/10-04-AAU.pdf