A declaration of war is Constitutional, legal procedure.
'Resolutions' and 'authorizations' are just a statement of policy....a.k.a. hot air.
See Article Article I / Section 8 / Clause 11
To declare War, grant Letters of Marque and Reprisal, and make Rules concerning Captures on Land and Water;
>> The formal statement of the warrant is to authorize the agent to pass beyond the borders of the nation (”marque”, meaning frontier), and there to search, seize, or destroy assets or personnel of the hostile foreign party (”reprisal”), not necessarily a nation, to a degree and in a way that was proportional to the original offense. It is considered a retaliatory measure short of a full declaration of war, and by maintaining a rough proportionality, has been intended to justify the action to other nations, who might otherwise consider it an act of war or piracy. <<
Declaring outright war is not superior from a civil-liberties’ perspective, but much more dangerous. The President has powers in times of war that neither the President nor Congress did not feel were necessary in several recent conflicts. To somehow quibble that a war is not legal because Congress only issued a resolution of war, rather than a declaration of war is to say that the President is impelled to suspend civil liberties whenever we must act to defend ourselves from foreign misbehavior. That is preposterous, and Paul’s implicit and accidental implication of such establishes that far from being the sole voice of reason and intellect he makes himself out to be, he is a dangerous fool.
Paul has provided a perspective which is valuable to have in the House on many issues, but it is a good thing that he will never be a serious candidate.