The last poll I saw showed that Cuccinelli had 68 percent support among Republicans. In a two point race, the problem here isn’t entirely with Libertarians. it’s with RINOs who will not support a conservative candidate.
In short, this is why the Republican Party is about to lose its base.
If the 3rd party wasn’t running, those voters would have to go somewhere. But I do see your point, RINO’s are a big problem too