You hit on a big issue in legal circles and jurisprudence classes when you said the Constitution was dead, which is does the Constitution evolve with the times? There are two schools of thought, both represented on the current SCOTUS.
There is originalism which fixes meaning to the constitution's text's public understanding at ratification, promoting stability. Gorsuch is a great example. Whether a layman agrees with his approach may depend on the issue. For example, the folks that generally left liked his concurrence when he voted against tariffs, even if the other justices in the majority didn't.
Living constitutionalism argues the document evolves with societal values and practicality, allowing for adaptation. Kagan probably is the best example of that. When it comes to the military action the courts have argued that the executive branch can act with greater speed, secrecy, and unity, which is necessary for responding to modern threats and warfare which require much more immediate action than threats in the 1700s. The other theme from living constitutional types is that Presidents have consistently engaged in military operations without formal congressional declarations (e.g., Korea, Libya, Iraq, Somalia, Serbia), creating a precedent that courts should not overturn.
I also might point out that this was Congressional action to not limit the President that just occurred, so it hard to argue that Congressional will is being thwarted.
