They couldn't just withdraw Yovanovitch, and needed to smear her in the process, because they had to discredit her, and her anti-corruption efforts, in order to effect their planned counter-revolution: rehabilitating the corrupt prosecutors and reinstalling a pro-Russian regime.
In doing so, they were, in fact, subverting official U.S. Government policy. To make it clear: Trump and Giuliani were deliberately undermining officially enunciated USG policy, and they were doing so for *personal advantage*, at the expense of U.S. national interests.
