One of Huckabee's pathetic excuses for David's apparent sadism was that the dog had mange.
The dog had an easily treatable skin infection, so it deserved to die.
Snopes has this:
http://www.snopes.com/politics/huckabee/dog.asp
Other media accounts here:
https://www.google.com/search?client=opera&q=david+huckabee+kills+dog&sourceid=opera&ie=utf-8&oe=utf-8&channel=suggest