Defamation requires some degree of lying to damage someones reputation, so this is not defamation.
Technically they suspended them for being elected and for the subsequent media interest, per their own words. Both of those things factually occurred. “Brought the party into disrepute” is a flimsy enough statement that it could hold as being a true belief regardless of circumstances, its not something that can be factually identified as a lie.
There is much that could be said about how fucked up what they’ve done is, but its also not defamation


