The Declaration of Independence had no legal standing in the Law of the United States. It is not part of any USC.
It is the very foundation upon which the entire edifice rests. The only way the constitution has legitimacy is if the Declaration is correct. If not, then our secession was illegal, and we should still be obeying English Law.
The Constitution is a consequence of the Declaration. Without our own independent government having some form of legitimacy, our Constitution doesn't have any legitimacy either.
The legitimacy of the US government from 1776 onwards, rests upon the premise that the laws of nature, and of nature's God give people the right to independence. No right to independence, no right to create a constitution.