This is basically not an issue at all (tip to Instapundit):
[Bill] Maher brought up Trump's pledge to kill family members of Islamic State terrorists. “That never even occurred to you, right?” Maher deadpanned.
“God, no!” [ex-CIA director] Hayden exclaimed. “Let me give you a punchline: If he were to order that once in government, the American armed forces would refuse to act.”
Maher responded incredulously, “What? Well, that’s quite a statement, sir.”
“You cannot—you are not committed, you are not required, in fact you’re required to not follow an unlawful order," Hayden replied. "That would be in violation of all the international laws of armed conflict.”
“You’ve given us a great reason not to support Trump. There would be a coup in this country," Maher cracked.
It would not under any circumstances be a coup--if by that you mean a measure outside of the Constitution to change the government.
It would not even be a revolt.
It would be the military following standard practice and rule of law.
As a new Army recruit, I was instructed on my obligation as a soldier to obey the lawful orders of those placed lawfully in command of me.
Remember, the post-World War II war crimes trials established the precedent that "I was just following orders" does not excuse you from being punished for committing war crimes.
So as a soldier, I was expected--even as a low-ranking troop--to understand that I am obligated not to commit war crimes, even if ordered to do so.
We can digress about how a low rank soldier is supposed to understand that, but killing civilians should be a no-brainer.
And those higher up the chain of command with access to lawyers and with plenty of education on what is lawful would have little problem with this issue, anyway.
So no, such a refusal by the military to obey a hypothetical order would not be a coup. I'm sure long before such an order was made public, higher ranking officers would explain that the president just can't do that.
And so no such order would be given.
UPDATE: At the Thursday night debate, Trump showed he just does not get this issue. It would be nice if someone explained to him that the military will--and must--refuse to obey illegal orders.
Of course, that's a target-rich environment, I admit.
UPDATE: I'm disappointed to hear people supporting Trump's desire to "take the gloves off" and kill our way to victory against the jihadis.
Let me point out two problems with that strategy that I set out when some wanted us to do the same to the Sunni Arabs fighting us during the Iraq War.
One, America could never be brutal enough to allow a strategy of annihilation to work:
I don't think our people back home would accept the killing of tens of thousands in a short time to brutalize even a uniformly hostile population into submission. Practically speaking, we could not be brutal enough for long enough to make Saddam's method of cowing civilans as he did to the Shias in 1991 work. I think we would make things worse by going back and forth between brutal methods to crush spirits and inducements to win loyalty. We'd just end up being brutal enough to inspire hatred yet generous enough to supply those hostile civilians; but not brutal enough to scare enemies into passivity or generous enough to buy friends.
Two, America should never ask our troops to be mass murderers:
In addition, our rules of engagement that promote winning hearts and mind allow our troops to fight with honor and come home as soldiers and Marines--not as killers. If we let our troops loose to kill as they see fit to terrorize the population into submission, they become judge, jury, and executioner. Even if they make all the right decision in a fight with enemies in civilian clothes, our troops will always wonder if they were right in the decisions they make.
Rules of engagement take much of the judging and responsibility out of their hands and put the responsibility on the leaders where it belongs. As long as soldiers know they followed the lawful rules of engagement they can come home with their heads held high, having fought as soldiers. As long as they allow us to fight and win, this is just fine.
There are enough militaries out there that specialize in brutalizing and slaughtering civilians. Our military is not one of them.
Oh, and if you want a third reason for not treating all of a group as an enemy when they are not uniformly hostile, which I couldn't possibly have noted at the time in June 2006, just months later our efforts to flip the Sunni Arabs of Anbar in the Awakening bore fruit and paved the way for a successful Surge offensive in 2007.