to answer one idiom with another, never say never. if a politician was sufficiently transparent about who they met with and took money from, acknowledged the potential conflicts of interest, documented decisions, sourced research thru firewalls, and generally had a system in place to prevent the temptation from manifesting, i'd be inclined to trust them
a good regulator might benefit from understanding the impact they're having, and that means talking to businesses. and an honest business that works with a bright and honest politician would have an incentive to help them stay in office, even if that money didn't buy them consideration. so there's potential non-corrupt reasons that these "donations" could happen
that said, i'm not claiming that hillary clinton, or any other politician that i'm aware of, has done this