No, because of the nature of the document. The Declaration of Independence is a legal document; the entire practice of law is built on practices which would be plagiarizing if found in a different setting. Just take a look at various state's criminal laws on a particular subject. You will find that many recycle the same phrases.
The difference is that when someone writes a book or article for publication, they are representing to their readers that they are responsible for the content and presentation, unless they specifically indicate otherwise. Authors of documents which carry the force of law, such as statutes and constitutions, are not representing that the ideas expressed are their own. Quite the opposite, in fact; the significance of those documents comes from the fact that they represent the opinions of either a group of people, or even an entire community. So