Whether Huck is to blame or not is irrelevant. Especially since there were a number of mistakes involved. However, this will come back to haunt him if he does indeed run in the primaries. Not just this incident, but his record in general involving these cases.
It will hurt his chances.
I think this will sink Huckabee's chances in any GOP primary.
Why?
Because the whole fiasco creates a very simple but awful narrative that fits into commercial sound bites.
It would go something like this:
"Huckabee commuted the sentence of a violent criminal. The criminal went on to murder 4 honorable police officers. Huckabee freed a cop-killer. Huckabee: soft on crime. Would you trust this man to keep us safe?"
Imagine that played over and over again on TV, and on the Radio, with grim music playing in the background. It's the scary sort of narrative that will stick in the minds of a public already nervous about crime and terrorism. It has a demon of a bad guy, and puts Huckabee on the side of the bad guy.
Considering that most voters often don't bother to dig too deeply into the issues, they are going to hold this against Huckabee, regardless of whether it is deserved or not.