I have to come to the Secret Service defense. Most of the issues that have surfaced are caused by a near-constant flip in senior leadership and decline of the culture and esprit de corps caused by that tumult. When setting video storage at 3 days, that's very likely designed to get rid of embarrassments of minor nature.
The agents I have worked with in the past, and there have been many, were top flight professionals. The flux in mid-level and senior leadership has to be addressed and a rebuilding of the culture of professionalism undertaken along with adequate funding to support that efffort. The negative incidents of unprofessional behavior and lapses in threat response get tremendous exposure on social media but overall the successes in defeating threats and avoiding exposures outnumber the negatives 1000 to 1 every single day, it just doesn't make for public interest.
When the culture returns to one of extreme pride and public recognition of their efforts then there won't be a need to delete video unless a "threat incident" occurred. Jus' sayin!