(From, appropriately enough, YellowTimes.org:)

... The other evening, a few old Texas Yellow Dog Democrats got together to chew the fat. There may be some readers who won't know the definition of a Yellow Dog Democrat. If the only candidate on the Democratic ticket is an old cur yellow dog running against an esteemed Republican, we'd vote for the Yellow Dog.

....

http://www.yellowtimes.org/article.php?sid=780