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.
The first amendment provides protection of the first essential conditions of individual liberty: the right to actively carry out matters of faith, conscience, in both public and private, to freely express oneâs beliefs, and perhaps of greatest important, the right to Assemble for any peaceable purposes ranging from religious, to political, to economic, to satisfying mere whimsy.