General Discussion

... authorized the president to exercise defacto war powers during times of "emergency", and in other conditions. For instance, there was never a declaration of war during the Vietnam conflict. It was euphemistically termed a "police action" if I remember correctly.

WWII, again, if I remember correctly, was officially declared by congress. I think it was the last conflict that was conducted under a specific "declaration of war".

There is a concern that modern warfare cannot be conducted under the rules laid out in the 18th century when the constitution was written. But the Alien Enemies act was also written in the 18th century, so it may be that the understanding of the time, that is, a formal declaration of war, may hold.