Sentence:  Because he spoke openly with what Channing had prophesied someone might - with daring hyperbole - Parker vindicated Channing 's further prophecy that he who committed this infraction of taste would promptly <WSD>discover</WSD> how little mercy liberals were disposed to allow to libertarians who appeared to them libertines . 
Meaning of the word marked with <WSD> tags:  get to know or become aware of, usually accidentally