US Secret Service - the United States intelligence agency that protects current and former presidents and vice presidents and their immediate families and protects distinguished foreign visitors; detects and apprehends counterfeiters; suppresses forgery of government securities and documents.
It's  blessings not blessing.. The entire clause is ...to secure the  blessings of liberty to ourselves and our posterity....    The blessings of liberty refers to all of the benefits that are  afforded by having liberty.
If the meaning of freedom has been a battleground throughout our history, so too has been the definition of those entitled to enjoy its blessings. Founded on the premise that liberty is an entitlement of all mankind, the United States, from the outset, blatantly deprived many of its own people of freedom.