1. People get the government they deserve. Police are a reflection of society.
2. People get the government they deserve. Cops do this because they know damned well that they'll get away with it. Ever notice that none of them are ever indicted/prosecuted? That's because, like literally every other institution in America, liberals control the justice system. A liberal prosecutor isn't going to indict a cop that is terrorizing the populace.
At some point, this is going to boomerang. The sooner the better.
http://www.veteranstoday.com/wp-content/uploads/2012/06/554728_392755290761978_704060660_n.jpg
This is a two party problem, not a one party problem.
There are plenty of law-and-order Republican judges who will support the cops in the name of law and order.