According to Google’s Transparency Report, the most significant spending from a single political campaign was the “Mike Bloomberg 2020 INC” campaign, where the spend accounted to $62.16 million. Throughout the campaign, Bloomberg’s team launched over 64,136 advertisements.
https://www.neweurope.eu/article/us-political-ad-spend-on-google-exceeds-384-mln-in-the-last-2-years/