The US Constitution is not a 'living' document or a 'dead' document, it is a legal document. It should be interpreted and applied as such.
If the US Constitution is a law (indeed, the law), who is the legislator?
According to the document itself, it is a political association known as 'We the People'.
Who, then, is 'We the People'?
Obviously it is us, the American people, embodied in either our state legislatures and Congress, or in state ratifying conventions and a Federal Article V convention, or some other proper mix of the two. The actual adoption of the original document demonstrates this form for us.
How should we use this knowledge to help us interpret the law according to the US Constitution? The same way we use knowledge of the proper method for adopting other statutes to do the same thing. When we wonder on the meaning of a law adopted by Congress, we look at the words and intentions of the draftees, of the legislators who vote to pass it, and the context in which it was passed.
Any other method of interpreting the Constitution is sophistic and almost always driven by a narrow political motive. We have reams of source documents on the drafting, discussion of, and ratification of the US Constitution. When we wonder what a particular clause might mean, we should look at what the state ratifying conventions were being told it meant by the proponents of the new Constitution. Just like we use reasonable understanding of the contractees when it comes to interpreting modern contracts, we need to look at the Constitution through the eyes of the people adopting it.
We have a hierarchy of source documents to turn to when it comes to understanding the Constitution:
1. Records of the state ratifying conventions and how particular portions of the document were explained to them
2. Records of the Philadelphia Convention which drafted the document
3. A more general understanding of the legal and constitutional atmosphere contemporary with its adoption. Remember, the people adopting the new US Constitution were veteran constitution makers, having already entirely re-made their own state governments at least once
4. General legal and constitutional English history and practice
5. Our own moral sentiments and rational constructions
To repeat myself, anything else requires an entirely alternative basis for political power and its derivation than the concept of democratic self-governance and democratic sovereignty that was concurrent at the time of the Constitution's adoption and (I would hope) is still the most popular political theory today.