From the Overview: "In the aftermath of the breach of the U.S. Capitol security on January 6, 2021--while a joint session of Congress was counting and certifying the 2020 presidential election electoral votes--and in response to increased political tension across the nation, there is renewed congressional interest in protective details for government officials. Attacks against political leaders and other public figures have been an ongoing 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). Prior to USSS protection, three sitting Presidents had been assassinated (Abraham Lincoln, James Garfield, and William McKinley). In addition, official records and news accounts show that there have been at least 20 attacks against Members of Congress since 1789."
CRS In Focus, IF10843
Congressional Research Service: https://crsreports.congress.gov/