Who is Kenneth Whistler from Jailbird and what is their importance?

In contrast, and perhaps even parallel, to the negative portrayals of idealistic capitalism (Nixon, Leen) is this character, an embodiment of the failure of idealistic communism - or rather, the failure of a man who preached the transcendent power of communism (for a description of Whistler's failure, see Chapter 20). The presence of Whistler, juxtaposed with that of Nixon and Leen (and the other manifestations of failed and/or corrupt capitalism), suggests the thematically relevant possibility that the novel is exploring the failings of not only capitalist idealism but communist idealism as well. In fact, it might not be going too far to suggest that the novel is, on some level, pointing out the failings of idealism in general.