For a moment last week, it seemed that leading US Republican presidential candidate Donald Trump had declared war on law itself.Then something shocking happened. Trump retracted (or, in political-speak, almost “apologized,” though he did not use those words) for statements he made about how he would fight terrorism.During last Thursday’s Republican debate, he said that he would order the US military to kill terrorists’ families.Trump made no qualifications about the families being actively involved or being willing to kill them as collateral damage when trying to target an arch terrorist.At most, he suggested that some terrorists’ families, or at least the wives of terrorists, know that their husbands are involved in terrorism. However, many family members don’t know, especially children, and even when they do know – and some do – passively knowing someone else is involved is not a capital offense, though it may be a crime.Trump also said, “We should go for waterboarding and we should go tougher than waterboarding” in terms of interrogating terrorists.Pressed on whether he really stood by these positions, Trump, as is his way, doubled- down.He even attacked rival Sen. Ted Cruz of Texas for waffling on supporting waterboarding, and confirmed his views in a separate television interview afterward.Then Friday he shockingly changed his tune.This from the man who has attacked every Democrat, Republican, reporter (even Megyn Kelly of Fox News) and pope who has gotten in his way and has refused to retract or back off.What happened that was so drastic that got Trump to back down, even if the retraction was a released written statement and did not come from him orally? Looking at the essence of his statement and at one of his notable critics sheds some light on the issue.Trump did not actually apologize or specifically retract anything. And he probably will try to press for fighting terrorism more aggressively than the Obama administration has. Rather, he reaffirmed his commitment to “laws and treaties” which the US is bound to and stated that he would not order “our military or other officials to violate those laws.”Many criticized Trump after his Thursday statements about killing terrorists’ families, who could be innocent, and about re-instituting waterboarding or worse (whatever that may be – the rack?), but two were very noteworthy.One was former US defense secretary William Cohen, who brought up the Nuremberg war crimes tribunals against the Nazis after World War II and explicitly said that Trump’s ideas could lead to valid war crimes complaints against the US.Cohen said the “notion that we would attack and kill the families of terrorists is something that contravenes everything the United States stands for... an order given by the commander in chief which violates every sense of law and order, international law and order” would be “a violation of the international criminal code.”But, at the end of the day, Cohen was defense secretary for a Democratic president and therefore his criticism is not what’s worrying Trump.Here was the real kicker.The Bush administration’s former CIA and NSA director general Michael Hayden said that if Trump, as president, were to order the US military to kill the family members of terrorists, “the American armed forces would refuse to act. You are required not to follow an unlawful order. That would be in violation of all the international laws of armed conflict.”Hayden is not merely not a Democrat, but he has been one of the Republican’s primary and most knowledgeable defenders of using torture or enhanced interrogation tactics, of the NSA collecting millions of bits of US citizens email and telephone meta data and of other aspects of the war on terror.And Hayden did not merely speak about “international law” in some theoretical way.He said that soldiers like him would refuse such orders because they violate “all” the international laws of armed conflict.There is really no such term as “all the international laws of armed conflict” in jurisprudence, so it is fair to say that, at a gut level, what Hayden really meant is that Trump’s statements put him at odds with something older than modern “international law.”Modern international law, especially since the late 1970s, has been hotly debated, and there are a variety of opinions about what it says on multiple different issues. Many even want to change it to take a tougher line on fighting terrorists.But there is an older body of law, often referred to as “the law of nations” or the “law of civilized nations” which was coined in 1758 and which has antecedents in medieval and ancient times, and relates to the principle of not attacking women, children or surrendered enemy fighters.In modern times, this is called customary international law. It is basically the Ten Commandments of international law that all but the most barbaric respect and agree on, even if they disagree about many other principles.This was the “all” that Hayden was referring to and the “laws and treaties” that Trump mentioned. That, and the specter of potential mutiny within the military, is what brought Trump to a dizzying and unusual about-face on Friday.