I think I have said this a different way but maybe he just wanted to see if he could make her cry. I have never hear that Trump fires people gently.The issue is not that he can’t fire an ambassador...he can as long as it is not for a corrupt purpose. Instead of just quietly reassigning her, he sent Giuliani and two thugs to initiate a smear campaign on her. These thugs, had energy related business interests in Ukraine and were illegally contributing to the Trump campaign in the process. One of the thugs has stated that he was on a secret mission for the president. Trump also felt the need to publicly harass (being kind) the woman calling her bad news, an object failure because of Somalia (????), and telling the president of Ukraine that ‘she is going to go through some things”. I think this is a bit bigger story than replacing an ambassador.