The Constitution is rigid. The interpretation of what is written in the Constitution is flexible.
Liberal judges have made it flexible, but it really isn't flexible. Consider the 14th amendment for example. Does anyone believe the framers of the 14th in 1868 intended to create a right to abortion? Or Homosexual marriage? Or Anchor babies?
It is this sort of deliberate misinterpretation of the intent of the writers of the constitution and it's amendments that undermine the rule of law.