From the Overview: "Due to the October 2018 attempted bombing attacks on current and former government officials (and others), there may be congressional interest in protective details for government officials. Congress may also be interested due to media reports of costs or budgetary requests associated with funding security details for the Secretaries of some departments or agencies, including the Department of Education, the Department of Labor, and the Environmental Protection Agency. Attacks against political leaders and other public figures have been a consistent security issue in the United States. Since the U.S. Secret Service (USSS) started protecting Presidents in 1906, seven assaults or assassination attempts have occurred, with one resulting in a death (President John F. Kennedy)."
CRS In Focus, IF10843
Congressional Research Service: https://crsreports.congress.gov/