It is an example of ideology-based passing on of data that fit a thesis and ignoring data that do not.
I have not done my own research on this but according to another source, the publicized recent shooters include:
- Adam Lanza - no evidence he is a Democrat and his mother Nancy Lanza was a registered Republican.
- Columbine shooters - claim that parents were Democrats not evidence-based.
- Eric Harris was from a military family.
- Dylan Klebold’s family was active in their Lutheran church.
- Nidal Hasan, the man accused the Fort Hood shooting, lived in Virginia or Texas, neither of which have registered party affiliations.
- Seung-Hui Cho of the Virginia Tech shooting was a Korean national with permanent residency status, not a citizen of the USA; he wasn’t eligible to vote in the U.S.
- James Holmes from Aurora was not registered to vote. Congresswoman Giffords’ shooter was a registered independent.