If it were NZ, we would expect the contestants to go into detail on their policies.
Talk about how they are going to solve relevant problems, how they are going to make the people safe, make the economy strong, how they are going to support business, provide healthcare, and how they are going to balance the budget.
But since it is US, I assume Trump will come up with nick names for his opponent, mock people, tell lies, blame everything on foreigners or Mexicans or Muslims or WHO or Obama. Declare that USA is doing the best ever, declare that he knows more than anyone about everything. Come up with some sort of chant "Build a wall", "lock her up" or whatever he thinks of. But provide no detail at all on anything.
Biden, I don't know enough about him to guess what he might say.