This might be one of Trump's "bombastic offers", meaning he wants tougher penalities for drug dealers so he starts with the bombastic offer to "begin the negotation". I don't pay much attention to Trump anymore, it's hard to tell when he says what he means, means what he says, believes what he says, or says what he believes.
As far as actually calling for the death penalty for drug dealers, it's pretty ridiculous. There isn't a direct act of force by the drug dealers to the people that are dying from taking drugs. So there's no death penalty.