There are multiple types of spoliation of evidence.  Most states recognize a negligent spoliation claim, though whether it is a separate tort is going to vary dramatically.  
Generally speaking, to actually obtain any sort of sanction in federal court where the action is on a federal claim, you have to prove the loss was in bad faith.  If it is a state law claim in federal court, where the rules of decision are state-based, that can change.
The issue is complicated here because these aren't courtroom litigants.  One of the remedies is an instruction from the judge that the other side is entitled to an inference that the evidence lost would have been adverse to the spoliating party.  But that is an instruction to a jury.
Here, the jury is the public and the GOP is arguing for that inference.  As we've discussed, I think it fair to do some investigation on it.  I just think that when you jump up and shout that it had to be intentional or in bad faith, but when at the end of the day you might have to admit it was negligent, then the impact of your claim is diluted.