Read this passage from Kennedy's Inaugural Address. Which lines refer to the Declaration of Independence?
...we observe today not a victory of party, but a celebration of freedom-symbolizing an end, as well as a beginning-signifying renewal, as well as change. For I have sworn before you and Almighty God the same solemn oath our
forebears prescribed nearly a century and three quarters ago.
The world is very different now. For man holds in his mortal hands the power to abolish all forms of human poverty and all forms of human life. And yet the same revolutionary beliefs for which our forebears fought are still at issue
around the globe-the belief that the rights of man come not from the generosity of the state, but from the hand of God.
..the belief that the rights of man come not from the generosity of the state, but from the hand of God.
For man holds in his mortal hands the power to abolish all forms of human poverty and all forms of human life.
For I have sworn before you and Almighty God the same solemn oath our forebears prescribed nearly a century and three quarters ago.

When President Kennedy relates the oath he has sworn to one that was sworn by the forebears almost 175 years before this, he is referring to the oaths the Founding Fathers prescribed when they wrote the Declaration of Independence.

Forebears in this instance refers to ancestors who would be the Founding Fathers and Kennedy was inaugurated as President in 1961 which was around the region of 175 years after the Declaration of Independence.