The United States is in theory, a Constitutional republic, of which, the highest law of this land, is its written Constitution. Further, this republic is divided into three separate branches, the executive, the legislative, and the judicial. However, when for all intents and purposes, the person that is in the executive office, is entitled to interpret law or to stretch law or to essentially make law in whatsoever manner that President desires to do so, and thereby to effectively circumvent judicial oversight, and to make irrelevant the making of Constitutional laws by the legislature of such, then this Constitutional republic has devolved into becoming an empire, controlled by the executive office, and none else.
For instance, only Congress has the Constitutional right to "…declare war," yet, as reported by Wikipedia.org, "On at least 125 occasions a US president has employed military forces without authorization from Congress." In fact, the United States Congress has not declared war on any other nation-state since 1942, so all of the wars that the United States has been actively engaged in since that time, as well as some of those before that time, have come about solely through the President using or usurping powers and thereby aggrandizing such into his hands, and thereby using American men and women, along with all of the military accouterments so demanded to make war against subject nation-states, that the President so desires to make war against; and in furtherance of such, superseding the need of a formal declaration of war to be made by Congress, of which the upshot of all this has even not precluded the President from implementing at his discretion, a wartime draft of its own civilians, without the need of a Congressional declaration of war.
Additionally, the President, without authorization of any legislative body or proper judicial oversight, or in conformance with international law and international treaties agreed upon, has in modern times, assassinated those agents of foreign countries that the President so desires to assassinate through the deliberate targeted killing of such; thereby indicating that treaties, international laws, and the sovereignty of individual nations, have no material effect upon the President, when it comes to the perceived right as interpreted by that President, to kill whomever the President so desires to kill, without an apparent limit to such.
It was not so long ago, that the United States, was a land of integrity of which the President of such, though believing that slavery was a grave moral wrong, did not believe that He, as President, had the Constitutional power to eradicate such; and it was not until the Southern States seceded from this Union of States, and therefore were in rebellion against its Federal government and its Constitution, that Lincoln was able to emancipate those held in slavery within those States that were in active rebellion against that national government, through his seminal Emancipation Proclamation, place into effect on January 1, 1863. Yet, in order to legally abolish slavery and erase such from this land, the 13th Amendment to the Constitution had to be written and thereupon ratified, so that slavery would no longer be constitutionally sanctioned.
The executive office of this country, though sworn to preserve, protect, and to defend the Constitution of this republic, has instead often deliberately violated that oath, and eviscerated this Constitutional republic, and therefore has wrested from the people their rights to the just powers as consented by those people, so that the President has become effectively above Constitutional law.