Wikipedia tells of the origin of the term "Yellow Dog Democrat".
"Let it be understood now and hereafter, that this is to be no joint debate," he said in that high-pitched shrill voice of his. "My friends have arranged for the use of this building and I intend to be the only speaker. But it is a tenet of our faith that in a Democratic gathering no man who calls himself a Democrat shall be denied the right to be heard. If the gentleman will be content to ask his question, whatever it is, and abide by my answer to it, I am willing that he should speak."
"That suits me," clarioned the interrupter. "My question is this: Didn't you say at the Louisville convention not four weeks ago that if the Democrats of Kentucky, in convention assembled, nominated a yaller dog for governor you would vote for him?"
"I did," said Hallam calmly.
"Well, then," whooped the heckler, eager now to press his seeming advantage, "in the face of that statement, why do you now repudiate the nominee of that convention, the Honorable William Goebel?"
For his part Hallam waited for perfect quiet and at length got it.
"I admit," he stated blandly, "that I said then what I now repeat, namely, that when the Democratic party of Kentucky, in convention assembled, sees fit in its wisdom to nominate a yaller dog for the governorship of this great state, I will support him — but lower than that ye shall not drag me!"
But lower than that, you will not drag me.