High on their own supply
By 
It’s, relatively speaking, comforting to assume that Trump and Giuliani were trying to smear Joe Biden with — in addition to the nonsense about Biden trying to get the Ukrainian prosector fired to protect his son (in fact the prosecutor was protecting the firm associated with Hunter Biden) — some even crazier conspiracy theory about how it was really the Democrats working with Ukraine who tried to steal the 2016 election, while making it appear that it was Russia who was intervening in Trump’s favor. (This is what all the wackiness about the “DNC server” being hidden in Ukraine is all about, if you haven’t gotten out of the boat).
The more disturbing possibility is that one or both of them are so far gone that they actually believe this happened. We’re talking about two semi-demented old men who have been exposed continually to the hardest core products pushed by the right wing fever swamp for many years now. (Replacement level Fox News junkies in other words).
The spectacle of Trump ranting about how we ought to execute whoever “smeared” him with an accusation that just yesterday the White House itself documented was completely true is of a piece with this latter view.