This is an excellent video covering the birth of the American ideal, as well as its perversion and degradation over time. The American Constitution is not, in itself, an invincible document. It does not provide freedom.
However, the Constitution IS a constant reminder of the responsibilities we the people must undertake in order to preserve liberty.
It is not the Constitution or the government which protects such rights, but the citizenry which is tasked with its own philosophical and moral prosperity. The American people are the first and last line of defense against tyranny.
The Constitution is not here to defend Americans;
Americans are here to defend the Constitution.