"Whose country is it?" joke

Found in Maps of the Mind, by Charles Hampden-Turner:
A man was hitchhiking across the country just prior to a
presidential election and had hit upon a technique for getting
free drinks in bars by guessing which candidate was less popular
and then loudly badmouthing them. He went into a bar in Colorado
and yelled, "Carter is a horse's ass!" To his surprise, he was
promptly thrown outside into the dirt. He picked himself up and
went into another bar, shouting, "Reagan is a horse's ass!" Seconds
later, he was eating dust again.
Seeing a cowboy nearby, he called out, "Hey, fella! If this ain't
Carter country and it ain't Reagan country, whose country is it?"
The cowboy replied, "Son, this is horse country!"