Lenin was unknown at the time... And so was Souvarine. Lenin didn't knew him, and even didn't knew that Souvarine had to fight in WWI from 1914 to 1916 (his brother died at war that year). The sentence has to be changed (and if not, deleted). I agree that the dispute is obscure, that's a problem... 

 You wrote  "He became associated with Totsky's Left Opposition". It's not true either. For reference, if you can read french, see the book by Jean-Louis Panné or - even better - the work by Charles Jacquier.