Let’s start with the beginning of the above mentioned document:

We the people of the United States, in order to form a more perfect union, establish justice, insure domestic tranquility, provide for the common defense, promote the general welfare, and secure the blessings of liberty to ourselves and our posterity, do ordain and establish this Constitution for the United States of America.

Note that the framers used the phrases (to pick just two) “establish justice” and “promote the general welfare” without specifying any definition of same, for they realized that it would be inappropriate for any constitutive document to try to frame such speifics that are better left to the legislative process. It is a strategic goal-oriented statement where the particulars were left for future generations to ponder.

What these terms mean and imply involves, by the very deliberate design of this minimalist document, future INTERPRETATIONS that must be made by each generation.

To argue that the courts or the executive or legislative branches must strictly construe the phase “establish justice” or the “general welfare” is, on the face of it, just drivilous. For there is nothing to construe, rather, there is something that must be defined by these branches in consultation with the people through a democratic process.

Thus political opposites like a Regan or Obama can both preserve, protect, and defend the Constitution, each in his own interpreted way, for there is no one timeless interpretation, strict or otherwise, of such an imprecise document.