We've seen the Trump campaign bring Benghazi moms, Bill accusers, now Obama's half brother. Now they're ominously hinting at 'surprise guests' we may see tonight. With the last one, you have to stop for a second and wonder if the Trump campaign is now so punch drunk from all the hits that they forgot who they're not running against.
However that may be, the key point is this. Hillary Clinton seems entirely unshaken by any of this. Indeed, it was a revealing moment when even Trump, asked for something good to say about his opponent at the end of the second debate, seemed to realize this himself, noting Clinton's doggedness and fight. She's simply unflappable. That may come at the expense of a guardedness or steely exterior which may hurt her in other ways. But Clinton is unflappable. There's simply no grounds for denying this.
We don't know specifically what effect having Mark Cuban at the events has had on Trump. But we do know that simply mentioning Alicia Machado at the first debate basically triggered Trump to blow up his whole campaign. Absolutely anything sets Trump off. He is the most manipulable, goad-able presidential candidate we've seen at any point in the remotely modern media era.
Like so much else about Trump, the whole storyline about 'rattling' Clinton or knocking her off her stride is entirely a story about Trump himself. It's entirely a matter of projection.