Have yet to hear an intelligent response to this.
I've seen several responses pointing out the errors. The Virginia Tech killer wasn't a US citizen and wasn't registered to vote, and even if he was, Virginia doesn't have party registration. Hasan lived in Virginia and Texas, neither of which has party registration. Breitbart retracted the claims about Holmes because they mixed him up with a different guy with the same name.
In short, whoever wrote it didn't really do their research. Several of these people were extremely mentally ill, a disease which doesn't respect political beliefs but has all too often lead to atrocities like this. We would do better to focus on keeping guns out of the hands of the mentally ill rather than poorly researched diatribes about depriving our fellow citizens of their right to self defense.