It can be argued, and proven, in a court of law that the United States does not have legal authority to be overseas. The War Powers Resolution has, in practice, ceded all Congressional authority in war-related matters to the Executive branch. This is akin to the President writing an executive order ceding Commander-in-Chief duties to the Supreme Court. The War Powers Resolution is a material change in the Constitution, violating the separation of powers, therefore is unconstitutional. That makes all overseas kills legal murders, ultimately at the hands of the Commander in Chief.
If each District Attorney in the United States filed charges of murder on each living president, the soldiers would become witnesses. "How many kills, soldier?" "Four." "Who ordered you to kill?" "Well sir, ultimately that would be President Clinton/Bush/Obama." "Thank you, soldier. Defense, your witness."
"Thou shalt not kill" is learned early as a child. "Kill, soldier kill" is a command followed as an adult. Emotionally, the soldier absolves responsibility and assigns it to his commander. However, that also puts the commander in the emotional position of God.
Make each President a hero, by sitting as a Defendant and being declared guilty of multiple counts of murder.