In order to use the API, you need to gain access to the Facebook Ads Library API at https://www.facebook.com/ID and confirm your identity for Running Ads About Social Issues, Elections or Politics, which involves receiving a letter w/ a code at your US address and sending picture identification to Facebook. [via https://github.com/minimaxir/facebook-ad-library-scraper]
Google
https://transparencyreport.google.com/political-ads/home - full data
CSV https://storage.googleapis.com/transparencyreport/google-political-ads-transparency-bundle.zip
Facebook
https://www.facebook.com/ads/library/
NO bulk download!
And this ...
Aggregation: 2019 EU Elections
Mozilla did collection https://adtransparency.mozilla.org/eu/
Not sure how to download the data in bulk though.
Very interesting log of the pain points in scraping Facebook API (which was very broken): https://adtransparency.mozilla.org/eu/log/