No it's not. They came up with the interpretation that the https://en.wikipedia.org/wiki/War_Powers_Resolution allows them to engage into limited armed conflicts without Congress authorization. Which is dearly needed, because that's what they are doing since decades, with the CIA and friends. And several such CIA wars happened even without the President's authorization, but usually the just lie to the president to able to engage in such armed conflicts.

What this War Powers Resolution does not authorize is a formal declaration of war (Clinton did not care) and any engagement voiding the Geneva conventions. All those drone killings are of course war crimes. This is one of the reasons the US does not recognize international law.

There are a number of reasons why this has happened. Some more nebulous than others. There are a number of extra powers granted to the Executive during a time of war that Congress didn't want activated. There are a number of requirements that kick in when war is "legally" declared that Congress didn't want activated as well.

I'm not saying drone strikes aren't shady, but they aren't strictly illegal. This is a case where Congress needs to get it together and start overseeing if they want it to stop happening. Otherwise, we're just left depending on diplomacy or the UN trying to put a stop to it, which likely won't happen either.

They are happy to use weasel words, this is a declaration of war:

https://www.govtrack.us/congress/votes/107-2002/h455