scalawag: a scoundrel; a political opportunist
The origins of this word are unclear, but it fits into the same category of outlandish insults as snollygoster. Although a scalawag (also spelled scallawag and scallywag) first meant any sort of rascal, after the Civil War it usually referred specifically to Southern white men who supported the government's Reconstruction efforts. They were often mentioned in the same breath with carpetbaggers—Northerners who arrived in the postwar South, carpetbags their only luggage, hoping to further their political fortunes. George Sala, foreign correspondent to England's Daily Telegraph during the war, describes the type in an 1864 dispatch: "The councilmen too often belong to the comprehensive genus 'scallywag'. They have intrigued and speechified, and stumped their ward." The word has not been used much since the early twentieth century.
On the ranges of the nineteenth-century West, scalawag was also a term for undersized or unhealthy cattle. The Oxford English Dictionary speculates that this usage might be the original one.