It can NEVER be fixed
All that data that's out there is out there forever. Facebook has no way of knowing who has copies, and has no way of knowing those copies were deleted. They have no way of knowing who else illicitly took data collected from apps and gave/sold it on for commercial use.
It is a safe bet that up to 90% of Facebook users (i.e. those who were on it prior to the time when they stopped allowing apps to gather data on friends, and hadn't gone through all the deep dark corners of menus to turn on all the privacy settings they could) have been hoovered up and are stored in one or more databases somewhere in the world.
Once they have that data, Facebook policy changes or user level privacy changes don't matter. It isn't like spam where you can decide you have had enough and change your email address and leave all the old spam behind.
It is safe to assume the RNC and its partners kept a copy of this data, and probably sought out other sources of similar data to increase the size of their collection. It is also safe to assume that if the DNC and their partners didn't get this sort of data for the last election, they are quickly trying to remedy that situation today in time for the fall election.
You can't stuff the genie back in the bottle, the only way it will ever be behind us is for everyone to abandon Facebook like they abandoned Myspace - but for that to happen there will have to be somewhere new for them to go (after all, Myspace wouldn't have been abandoned if it wasn't for Facebook) No doubt this replacement will want to make more money and end up making the same mistakes, unless some rich billionaire who feels bad about the harm he's caused the world (hey Zuck, you listening?) starts one as a non-profit that doesn't take ads and maintains strict privacy controls.