"Legit war time measures" is not a thing. If Congress declares war on Cuba or Venezuale for example, people who do not support it will not see the measures as "legit". The US has a lot of precedent of bombing/invading other countries at the whim of presidents without actually calling it a war for decades.

And for better or worse, it is actually good that it is like this. Otherwise, if Congress declares war on Iran or China or whatever, the whole country will be put on a war footing, companies will be directed to build whatever the Pentagon says it needs, drafts will be enforced and so on. And it would be pretty ugly.