"Liddle" is baby talk for "little".

In English, people talk to babies affectionately in a kind of nonsense language. I don't know if you also do this in China. Probably! I expect adults do this in all cultures in the world. There are probably some nonsense words in Chinese that people use to talk to babies (and also to cute animals).

https://en.wikipedia.org/wiki/Baby_talk

Quote from Wikipedia:

"When adults talk to each other using baby talk it is generally to either show affection by emulating the fondness shown by adults for children, or as a form of bullying or condescension"

In this context, I expect Mr Trump is bullying the gentleman in question.