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.
Deprivation of Liberty Safeguards. Liberty means being free to do the things you want to do and live where you want to live. Deprivation of liberty means taking someone's freedom away. A recent Supreme Court judgement decided that someone is deprived of their liberty if they are both 'under continuous supervision and control and not free to leave'.