I didn't see the video, but I can see Trump saying this in a mischievous and ironic way because he himself is quite the maniac when setting the stage for what he wants, and he often gets great things done as a result. In other words, Trump is able to be a maniac AND get things done.
But looking at Cruz's inability to get many things done in the Senate at least backs up what Trump is saying about Cruz. Trump may be saying Cruz is a maniac, but his main point, or verbal kill shot, is that Cruz has a weak record of getting things done, especially if you look at his work in the Senate.
If “get things done” means “put casinos into bankruptcy” or “inherit a fortune from my daddy”, sure.
Name ONE policy Trump has proposed “since” he started running for president that is going to received by Congress any better than Cruz’s policies?