Citizens United is widely considered the event that would cause US corruption to spiral out of control, but there was always the hope that a constitutional amendment could get us out of this.

Neither side ever even attempted it. Every once in a while you get some lip service about small money donations but nobody ever tried to go after the problem at the root in all this time. Think about what that means.

Some local governments are fully designed to be perfect vehicles for corruption by this point. The incentives just lead to it over time as one corrupt prick makes things a little easier for themselves and their ilk to operate without oversight. Things compound over the decades of people drawn to the graft opportunities in local government with their campaigns funded by the beneficiaries of the graft, against little to no opposition.