Violent crime has not dropped 12%, so don’t bother looking for explanations. This will turn out to be due to either a change/screw-up in reporting procedures or a bureaucratic redefinition of what counts as a verified “violent crime”.
Nope. Violent crime has been dropping for many years now. There are other factors at work, some mentioned in this thread (more citizens legally armed, demographics, etc).
And while half the country does vote for Democrats, the general attitude towards crime has been generally much tougher over the last couple decades. We incarcerate criminals at a fairly high rate and the public simply isn't as tolerant of criminals as it was in the 60's and 70's (when the thinking was to rehabilitate rather than punish). 3 strikes laws, for example, were a response by the citizenry (through their legislatures) to liberal judges; mandatory sentencing and stronger sentencing guidelines also followed due to angry citizens demanding these new laws from their elected representatives.