Donald Trump likes to ridicule opponents with nicknames. Lyin’ Ted Cruz. Mini Mike Bloomberg. Pocahontas Elizabeth Warren. He uses these nicknames because he thinks they are effective.
The reason he is convinced that they are effective is most likely personal experience. Trump went to a military academy for high school. He was either taunted there or taunted others. Probably both. He didn’t like it and when he saw how nicknames helped him bully others he got religion.
If his opponents were smart they would try to find a few people Trump grew up with. Ask them for the nicknames Trump was taunted with as a kid. Then use them against him or use them to negate his use of them.
But if they were smart enough to do that they would have done it already.