In answer to the query about useful sources on Mark Twain and P. T. Barnum--
I highly recommend Neil Harris's book about Barnum, _Humbug: The Art of
P. T. Barnum (Chicago: Chicago UP, 1973).
While it's only about Barnum, Harris does a really good job locating Barnum
in the cultural context of nineteenth-century America. The book would, at
least, give you some useful background for speculating about connections
between them.
Susan Reed