The CIA wasn't successful in killing Fidel Castro, either.

It's the intent that counts!

Again, we have been at war in Korea since the 1950's; no 'declaration' is needed.

Just as there was no 'declaration' necessary before we bombed Libya or before we bombed Syria.   President Obama made the decision and bombed.

President Trump didn't have a 'declaration' before the 59 Tomahawk cruise missiles attacked the Al Shayrat Airbase in  Syria, either.  That was in April of 2017.  

How many US soldiers and foreign civilians have died in how many wars since the last "Declaration of War" by the US in 1941?

The Gulf of Tonkin "Resolution"?  The Bush Iraq War "vote"?  

President Obama attacked Syria and Yemen and Libya with nothing but the Bush vote to rely on and his own decision that it was a good idea to do all three attacks.  

You are wishing for something that the US Senate gave up requiring over 50 years ago.