Trump has long held tension and resentment against Zelensky. This time Zelensky publicly criticising Trump for his decision to ease sanctions on Russian diesel ( Z criticism understandable) has triggered him yet again.
Trump hates public criticism, it's a personal injury to his fragile ego and his image of himself. He sees himself as superior and more powerful than Zelensky. Trump's habitual behavioural response is to belittle, hit out and injure and humiliate Zelensky in return. He tells Z to stop attacking Russia's oil refineries- to cower Z. He calls for Z to be replaced - to humiliate and belittle him.
All this, to make himself feel better with no care for the impact on Ukraine and its vulnerability against Russian aggression.
Shameless and shabby. That a US president behaves in this way is extraordinary. However, sadly the world has become accustomed to Trump's outbursts. Hopefully though- never immune to his despicable behaviours.