They said that Hillary...
This is not really a Trump meme - it is a meme making fun of that guy that can't remember the name of anything. He is a politician in that party that is opposed to the party that that other guy is a part of.
It is sort of funny, but only of you know who Biden is, and know that he is known for not being able to come up with the right word.
The reason why it is funny is that it is making fun of someone, and insults are humorous.