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.
As believers in Jesus Christ, we who are the bride of Christ wait with great anticipation for the day when we will be united with our Bridegroom. Until then, we remain faithful to Him and say with all the redeemed of the Lord, Come, Lord Jesus! (Revelation 22:20).