IMO, the key to understanding Trump's behavior in this regard is his narcissism, his intense concern over the legacy he is going to leave behind him and his innate cowardliness that he hides by faking his bully boy persona in whatever room he finds himself in.
He's a spoiled brat man-child trying to behave as the stable genius he'll never be. Taken to the edge of being held responsible for the death of thousands of our own armed forces, even with foreknowledge of what was about to transpire and the eventual escalation that follows, it seems to me that as others have mentioned, it was a staged event with a predetermined outcome or an act of cowardliness when faced with an outcome and the inevitable follow-on future events that Trump realized would be completely out of his control the moment he pulled the trigger.
He likes to appear to be, as Bush Jr. said "The Decider" in all things that affects his ratings and his legacy. Having to start a shooting war, where it's common knowledge that "a battle plan never survives the first encounter" and where, to Trump's worst fears he will then have to rely on others to determine the outcome of anything that happens after he gives the go word it just seems natural that Trump would refuse to put himself in that kind of position.
His fate will then be in the hands of others. That's coming straight out of Trump's worst nightmares. I really don't think he'd be able to allow that, his being the prototype control freak that he is.