Once upon a time, there was a snake who at the end of a path wanted to cross a river. The river was raging, and it looked hopeless.
Along came a horse down the path, looking to cross that river. The snake said “HEY! Could you help a brother out?”
The horse was accommodating. He carried that snake across that river safely to the other side, where he dismounted and promptly bit the horse.
The horse was dumbfounded. “Why did you bite me?” he asked.
The snake replied “I’m a snake, stupid.”
Indeed, as one might trust those who are recipients of favor, there is a fairly consistent expectation that simply feeding an alligator wont protect you when he is hungry again. In this case of carrying the snake, its in his nature to bite.
So it is with the left. Its in their nature to act contrary to what conservatives might like or appreciate. The danger of associating too closely can hurt, but even worse, after carrying their goals across raging obstacles, the would-be conservative might find there is no warmth or gratitude. They will still bite, and perhaps even ask for a ride back to where they were.
Republican political leadership often thinks that this will change at the next crossing. Inviting the snake of the left to ride along with their successes, and in many cases making successes of what it is the snake wants. Counting on the snake to behave, offer reciprocal assistance in some way, or even feel guilt for its poison effect. The snake for its part feels no loyalty; for it is a snake, and that is just how it is.