contemptuous nickname in U.S. politics for Northern Democrats who worked in the interest of the South before the Civil War, by 1833. It was taken to mean "man who allows himself to be molded," but that probably was not the original image. The source is an 1820 speech by John Randolph of Roanoke, in the wake of the Missouri Compromise.
Randolph, mocking the northerners intimidated by the South, referred to a children's game in which the players daubed their faces with dough and then looked in a mirror and scared themselves. [Daniel Walker Howe, "What Hath God Wrought," 2007]
Randolph had used the term dough-face in the sense "mask of dough" in Congressional debates as far back as February 1809 ("... it is something like dressing ourselves up in a dough-face and winding-sheet to frighten others ....").
However, the expression has been explained as referring to "the pale doughy faces of his frightened opponents" [Craigie], to a "person who is pliable and, as it were, made of dough" [Century Dictionary], or even "to liken them in timidity to female deer," which is frightened at her own shadow [The Port Folio, 1820]. Dough-faced in the sense "cowardly" is attested in a text from 1773, so there might be a convergence of senses.