Its interpretable -- its language is broad in many places such that a range of actions can fit under its terms. For example, what precisely does it entail to "provide for the common Defence and general
Welfare of the United States"? This is a changing concept.
Interpretation of the Constitution has only been used to back up a certain political agenda. For example, during the New Deal, the Commerce Clause was interpreted to mean Congress could regulate commerce within states, when it's clear that the Commerce Clause gives Congress the power to regulate interstate commerce. Same with the "General Welfare" clause, which has been used to interpret health care and other BS as being Constitutional.