I'm going to guess you know even less about how prisons function in the U.S. than you know about climate change. I spent nearly a decade working for the Department of Corrections in the State of California. This is where you get to view me as an expert on the topic, while you are merely sitting in the peanut gallery tossing out links that don't paint an accurate picture of prison operations in the U.S.
First, in regards to the OP, I do not believe the majority of criminals identify as Democrats. I would guess that almost the entire prison population has never voted or could tell you the difference between a Democrat and a Republican.
So people actually need to do studies to prove that the longer you lock someone up, the more they become institutionalized and the more they learn trade craft from other inmates, and the more likely they are going to become recidivists. Brilliant. Also, whatever recidivism rates prison administrators are giving out, you can bet the actual rates are higher. A significant number of inmates are released from prison and then they go live with a relative in another state, where they begin committing more crimes. The state they were locked up in will likely not call them a recidivist. The same holds true about the many convicts who get out of prison and soon after are murdered. They are considered non-recidivists. Then there are the following statistics; a burglar averages 20 burglaries for every time he gets caught once. He gets arrested 5 times, on average, before he is convicted and sentenced. So he may get away with nearly 100 burglaries before he goes to prison. That's an average burglar. A good burglar can make a fairly successful career out of breaking into homes. So when a guy learns a few new tricks in prison and gets out of prison, he can keep being a criminal for decades without being caught. Again, he's not showing up as a recidivist.
Most prisons are warehouses. They quit wasting money on rehabilitation programs years ago. It's because prison populations have changed dramatically. The criminal justice system is so overloaded in the U.S. that they do everything they can to avoid sending low level criminals to prison. But what they consider low level prisoners are people who would have gone to prison for years a couple of decades ago. Our cities are overflowing with violent predators who have been released from prison after serving only part of their sentences. They use to call it good behavior. Now, as long as you don't murder a prison guard, you are considered to have good behavior. The prison population in the U.S. is made up primarily of the worst of the worst. Violent sociopaths. Men you never want to cross paths with.
European prisons are more like Disneyland. Boatloads of mostly non-violent offenders. Drunks and drug users and thieves. The sort of offenders that are put on probation in the U.S. Part of the reason is they don't all carry weapons. Guns are used to resolve a lot of differences in the U.S. Sometimes even petty disagreements are resolved in a hail of gunfire. I saw two guys at a Circle K buying gas, who got into an argument over who was going to win that nights televised middle weight fight. The argument ended in murder. Seven blocks from our home, two young men involved in the drug trade, settled a dispute by pulling pistols and firing at each other. After 12 rounds, one was dead and the other will be spending the remainder of his life in prison. These stories are typical in the U.S. and almost unheard of in Europe. Again, they don't have much to do with politics or political parties.
The answer is not to reduce sentences in hopes of reducing recidivism. The answer is to keep these monsters locked up as long as you can. Taxpayers overwhelmingly support building as many prisons as it takes. However, there is a way to reduce the cost of incarcerating violent criminals. We could ask Mexico to construct a series of prisons along their northern border and ship part of our prison population to them. Allow human rights organizations to approve of the prison and make sure inmates are getting their meals and medical attention. You'd probably reduce the cost of housing inmates by over 50%.
