Notice that they mention in the video report on that page that they have been looking into his electronic communications involving contact with minors.
The presidential protection detail is a relatively minor part of what the Secret Service more broadly does...
https://en.m.wikipedia.org/wiki/United_States_Secret_Service#Domestic_expansion
The Secret Service also investigates missing and exploited children and is a core partner of the National Center for Missing & Exploited Children (NCMEC).
...
The USA Patriot Act, signed into law by President George W. Bush on October 26, 2001, mandated the Secret Service to establish a nationwide network of ECTFs in addition to the one already active in New York. As such, this mandate expanded on the agency's first ECTF—the New York Electronic Crimes Task Force, formed in 1995—which brought together federal, state and local law enforcement, prosecutors, private-industry companies, and academia. These bodies collectively provide necessary support and resources to field investigations that meet any one of the following criteria: significant economic or community impact; participation of organized criminal groups involving multiple districts or transnational organizations; or use of schemes involving new technology.[31][32]
The network prioritizes investigations that meet the following criteria:
Significant economic or community impact,
Participation of multiple-district or transnational organized criminal groups,
Use of new technology as a means to commit crime.
Investigations conducted by ECTFs include crimes such as computer generated counterfeit currency; bank fraud; virus and worm proliferation; access device fraud; telecommunications fraud; Internet threats; computer system intrusions and cyberattacks; phishing/spoofing; assistance with
Internet-related child pornography and exploitation; and identity theft.
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