Who provides security for United States senators?

Protective Services (bodyguarding) for members of U.S. Congress and the Senate are provided by the United States Capitol Police, unless the Senator or Congress person has a different protected status, such as the when Hilary Clinton was the Senator from New York. Senator Clinton received protection from the United States Secret Service because she is a former First Lady of the United States and is entitled to receive protection until she passes on or declines the protection.

Then Senator Clinton now Secretary of State Clinton now receives protection from the Diplomatic Security Service. Once she leaves office she will regain her Secret Service protection.