In a Mises Institute condensation, titled, “The American Empire,” (CC BY-NC-ND 4.0) from Garet Garrett’s book, The People’s Pottage, he wrote,

The extent to which the original precepts and intentions of constitutional, representative, limited government, in the republican form, have been eroded away by argument and dialectic is a separate subject, long and ominous, and belongs to a treatise on political science.

…When the process of erosion has gone on until there is no saying what the supreme law of the land is at a given time, then the Constitution begins to be flouted by executive will, with something like impunity.  The instances may not be crucial at first and all the more dangerous for that reason.  As one is condoned another follows and they become progressive…

Garrett describes a representative instance of the whole erosive process,

…There was one thing a President could never do.  There was one sentence of the Constitution that could not fall, so long as the Republic lived.

The Constitution says: “The Congress shall have power to declare war.”

…Congress could be trusted never to do it but by will of the people.  And that was the innermost safeguard of the republic.  The decision whether or not to go to war was in the hands of the people – or so they believed.  No man could make it for them…

He writes that this constitutional principle was circumvented, an example of the progressive ‘revolution within the form,’

President Truman, alone and without either the consent or knowledge of Congress, had declared war on the Korean aggressor, seven thousand miles away, Congress condoned his usurpation of its exclusive constitutional power.  More than that, his political supporters in Congress argued that in the modern case that sentence in the Constitution conferring upon Congress the sole power to declare war was obsolete.

Mark you, the words had not been erased; they still existed in form.  Only, they had become obsolete.  And why obsolete?  Because war may now begin suddenly, with bombs falling out of the sky, and we might perish while waiting for Congress to declare war.

The reasoning is puerile.  [Firstly,] the Korean War, which made the precedent, did not begin that way; secondly, Congress was in session at the time, so that the delay could not have been more than a few hours, provided Congress had been willing to declare war; and, thirdly, the President as Commander-in-Chief of the armed forces of the Republic may in a legal manner act defensively before a declaration of war has been made.  It is bound to be made if the nation has been attacked…

A few months later Mr. Truman sent American troops to Europe to join an international army, and did it not only without a law, without even consulting Congress, but challenged the power of Congress to stop him.  Congress made all of the necessary sounds of anger and then poulticed its dignity with a resolution saying it was all right for that one time, since anyhow it had been done, but that hereafter it would expect to be consulted.

But the damage had been done.  The congress no longer held this constitutional power, de facto.  All that was left was for the executive branch to declare it de jure.  Garrett writes,

At that time the Foreign Relations Committee of the Senate asked the State Department to set forth in writing what might be called the position of Executive Government.

The State Department obligingly responded with a document entitled, “Powers of the President to Send Troops Outside of the United States, February 28, 1951.” For the information of the United States Senate, it said: “As this discussion of the respective powers of the President and Congress has made clear, constitutional doctrine has been largely molded by practical necessities.  Use of the congressional power to declare war, for example, has fallen into abeyance because wars are no longer declared in advance.”

…If constitutional doctrine is molded by necessity, what is a written Constitution for?

Garrett states that the modus operandi for every revolutionary act undertaken by the Wilson, FDR, and Truman administrations, in the context of his example,

Thus, an argument that seemed at first to rest upon puerile reasoning turned out to be deep and cunning.  The immediate use of it was to defend the unconstitutional Korean precedent, namely, the declaration of war as an act of the President’s own will.  Yet it was not invented for that purpose alone.  It stands as a forecast of executive intentions, a manifestation of the executive mind, a mortal challenge to the parliamentary principle…

If you think about recent history, this method of operation is used to this day at all levels of government.  Imagine teaching these things in civics class.