Wars are supposed to be publicly debated. The purpose of this is to avoid wars which the public doesn’t understand and focus on critical fights, not Presidential whim.
When was the last declared war?
Every war the U.S. has fought since World War II was basically a "colonial" war. This means there's no way to effectively defeat the enemy from a traditional standpoint when the sole purpose of the military campaign is to turn the enemy into suppliers and customers of global industries. There's no reason to lay waste to entire nations when the whole purpose of engaging them militarily is to transform them into trading partners.
We have had ZERO wars fought by us since WW2. Congress has not declared war on anybody since WW2, for the simple reason that Article 2 section 4 of the UN Charter forbids us to do so without UN approval. It has all been "police actions" or "authorization for the use of force".
We have not had victory, because we have not waged war. War involves the destruction of the enemy's capabilities to the point where they are forced to surrender or face extermination -- which were the choices given to Germany and Japan in 1945.