Trump must be winning big in the internal polling. “going negative” is a tactic losing campaigns try as a “Hail Mary” play to try to turn things around. if you are winning, you “go positive”.
For example:
"First on CNN: New Cruz ad hits Trump's character, accuses him of 'sleaze' CNN ^ | 2/11/16 | MJ Lee Posted on 2/11/2016, 3:59:45 PM by TBBT"