They are allowed to do that privately, of course. However, the general influence of police forces on politics is low to zero here. A local police officer (for example, in a small town / village) doing local politics would seem quite strange.
There is of course some influence of police unions on the departments of interior of the states (Länder) and the federal government (Bund), but this is more like an employee complaining to their superior about low-level problems that could be fixed by legislative changes. It is almost never done publicly.
> Some of the unions have been known to openly attack with billboards, having squad cars follow, and more, candidates who seek to reform policing and pension benefits; benefits which are excessive on any level of sane measurement.
If something like that (police cars enforcing a political agenda) would happen here it would almost certainly be national news instantly, and the officers would most certainly (and rightfully so) loose their jobs. We had some bad experience with stuff like that not too long ago :)
I think the US is suffering from the disadvantages of decentralization. Local police forces have much more freedom and get away with a lot of stuff. The training is also very inconsistent and generally not sufficient.
Also the fact that sheriffs and judges get elected seems to have the opposite effect from the intended one. Instead of more accountability this seems to lead to less accountability and there is less professionalism.
There was an attempt to import the American system by establishing "police and crime commissioners". They are absurdly highly paid compared to most political appointments (especially councillors they replaced): https://www.bbc.co.uk/news/uk-22624096 - but they remain pretty invisible in the news. My pet theory is they were created to establish a funding channel to Conservative party candidates.
All shootings by police are routinely investigated by the fairly independent IPCC.
(The one big exception to all this was the history of the RUC in Northern Ireland, which is a whole other story)
Policing in Italy is still mostly stuck in the “authoritarian” phase, for umpteen reasons that would be tedious to list here. Suffice to say that a country where the largest police force is effectively military police, is not exactly a model.
https://www.dutchnews.nl/news/2018/09/minister-tries-to-have...
Yes, I know this contradicts the parent, but the US is large, and every place is different.
So the excesses simply are the filtering down effect as judges are appointed in many areas by the same politicians who are under the thumb of these two very powerful political forces. After all, you can just imagine the FUD they can dispense for anyone who dares cross them.
* note, I listed police and sheriff separately because the sheriff side is more commonly associated with prisons; California's sheriffs union is a notorious cause of the growth of that system. they are just that powerful