Trump can only throw barbs and innuendos because he can’t debate intelligently on the real issues and present coherent solutions!
His emotions get in the way because he's hard wired to his audience's where he controls the stage and can feed off their attention.....In a debate he shares a stage with several “powerful” men that he knows full well know more than he does and he has no attorneys at his side to step up as he does in business deals.... He's on his own....and that's why for so long we've heard him spill out word salads that overlap each other...he's flustered inwardly.
However, in this last debate he was far more prepared and coherent than any other....which shows his coaching worked and or he's finally catching on....probably both. He needs to show himself as Presidential, contrary to what some might otherwise think. That debate was the closest he's come to that in a public forum as this.