From a WaPo article (“Final volume shows why Twain wanted ‘Autobiography’ kept under wraps“):
Only with the publication of this, the third and final volume of his “Autobiography,” do we finally understand why Mark Twain wanted the book kept under wraps until 100 years after his death. He did take potshots at various targets in the first and second volumes, but most of them were minor figures hardly remembered today. (He’s probably right, for example, to charge that Bret Harte’s meager talent burned out after he wrote four or five memorable short stories, and that late in his life Harte became a sponger, but who really cares now?) In Volume 3, however, Twain is at full cry in pillorying two of the most widely admired 20th-century Americans: the eternally adolescent Teddy Roosevelt and the vainglorious Andrew Carnegie.
At one point, Twain vilifies TR by comparing him to the vilifier’s own most famous creation: “Mr. Roosevelt is the Tom Sawyer of the political world . . . always showing off; always hunting for a chance to show off; in his frenzied imagination the Great Republic is a vast Barnum circus with him for a clown and the whole world for audience.” Elsewhere, Twain calls Roosevelt “the missing link,” i.e., the supposed evolutionary place-holder between the ape and homo sapiens.
When conservatives I know resist the idea of Trump as POTUS, I remind them of TR, a bloviating self-promoter who, whether you agreed with his policies or not, has become one of America’s “great” Presidents.