The Secret Service

The Secret Service was originally started by Abraham Lincoln, ironically on the day he was shot, to deal with counterfeit currency. As is usual for bureaucracies their duties expanded to the protection of the President after McKinley was assassinated in 1901 and for some unknown jockeying of power reason took on the Bureau of Alcohol, Firearms and Tobacco in later years as well.  Apparently the AFT was peeled away from the Secret Service recently, why wasn't their original mandate to protect the financial system rationalized away from the as well? Their executive protection mandate is sufficient.  Why spread the Secret Service thin on issues that other agencies are more attuned to and better equipped to handle?