According to the Yale Book of Quotations, the Disraeli theory is
supported by a July 27, 1895 attribution in the London Times,
strengthening the claim by Twain. Robert Giffen uses a similar quote in
a June, 1892 Economic Journal article.  And there are other citations
that attribute it or something similar to "the Wise Statesman" or "a
witty statesman" that the Yale entry says could strengthen the Disraeli
theory. 

I just saw something else called The Quote Verifier that puts some doubt
back in the Disraeli theory.  It adds a bunch more usages and other
possibilities of who said it first, including "a recent President of
Harvard" (1896) and Tennyson.  

Mathew Forstater