When has he ever shown it? In all his speeches and all his interviews he has rambled and bragged and made wild promises, generally over the course of a few minutes. What passes for debates in our presidential election cycle are like nothing he's ever done before. He will be on stage facing an audience, a sizeable percentage of who don't think he has the gravitas to be president, and have to deliver a clear, concise message in a short period of time. I don't think he can do it. I fully expect Trump will demonstrate that lack of stature for the office for all to see. And I fully expect Ted Cruz to blow the doors off the place. And come August 7 then I think you'll see Trumps numbers dropping and Ted Cruzs numbers shooting up.
As a former New Yorker, I've seen him in many, MANY interviews over the years and he can be brief when he has to.
I wouldn't predict with any certainly that he will go one way or another in the debates.
It will be interesting to see how his stage presents compares to other candidates. I don't remember seeing him actually share the stage with anyone else.