How? Which political party or independents promote a policy to reduce police powers?
And even if there were, or are, any politicians with such a policy we ought to be more suspicious of them!
Policing is mostly local, so I think this is an area where there's a real chance to make things better. National politics are hopelessly tribal in the US, but city/county level politics are much less so. Go to city council meetings. Pay attention, and complain if they try to buy leftover military hardware like a BearCat[1]. Vote for and talk to your councillors. Organize a petition to de-militarize your local police force.
It's not "reducing police power", it's "even better training, tools and techniques for our hard-working police officers".
Aren't you assuming that people want something better? I don't know if that is true. Many people refuse to believe cops can be bad (due to ignorance or whatever other reasons)