They know Trump is heavily favored to win in 2020.
Just another ploy to delegitimize his presidency. "A rational voter base wouldnt elect him. He must have cheated."
It's way more basic than what you say.
The strong prey on the weak for fun. For three years the Dems have abused Trump at will. His response is to cry like a pussy on twitter all day long.
Why would they stop abusing this weakling when they are getting the response they hoped to get?