I don't think it's about the US in its entirety, nor ads, but Republicans and Elon Musk have become very skilled at exerting political influence in the US [1] and Europe [2] through social media in ways the public isn't really aware of:

[1] https://www.techpolicy.press/x-polls-skew-political-realitie...

[2] https://zenodo.org/records/14880275