A quick “gloss” primer: Justice Felix Frankfurter introduced the idea in his 1952 Steel Seizure Case concurrence, arguing that “[i]t is an inadmissibly narrow conception of American constitutional law to confine it to the words of the Constitution and to disregard the gloss which life has written upon them.” He wrote:
a systematic, unbroken, executive practice, long pursued to the knowledge of the Congress and never before questioned, engaged in by Presidents who have also sworn to uphold the Constitution, making as it were such exercise of power part of the structure of our government, may be treated as a gloss on ‘executive Power’ vested in the President by § 1 of Art. II.
Executive branch lawyers rely on this idea when crafting opinions about the legality of presidential action, including military intervention without Congressional authorization. The history of past military conflicts informs their analysis of whether a new unilateral military intervention is within the scope of presidential power. In practice, each conflict becomes a building block for the next one, expanding the legal basis for unilateral presidential power.
This analysis relies on history, but the underlying history is not subject to revision. Because such opinions are often classified, transparency and external criticism are hampered.
The Korean War is an example of the reliance in law on outdated history. President Harry Truman minimized the conflict, refusing to call it a “war.” My research shows that he did not seriously contemplate whether to ask Congress for a war authorization until after U.S. troops were in battle, and then proceeded without Congressional authorization for political reasons. He also ordered U.S. military engagement before the U.N. Security Council authorized it, even though the administration later pointed to the UNSC resolution as providing legal authority for war. The contemporaneous legal document most often cited on the legal basis for the war, a 1950 State Department opinion, curiously was edited when published in a way that obscures the timing of Truman’s action in advance of the UNSC.
Although Truman justified his action by minimizing the war, calling it a “police action,” in the end, the conflict resulted in 2-3 million deaths. Many were civilian casualties from U.S. aerial bombing – the U.S. flew over a million sorties and dropped 386,027 tons of explosives. If a conflict with that level of destruction was not a “war,” then the concept of war has no meaning.