The German chancellor stated the facts that the US has no plan for how to end the Iran war, their negotiations are a shambolic mess, and the US is being humiliated by the impotence and incompetence of its government.
Trump got asshurt and took to social media to make sure the entire world knows that he has no control over his emotions and threatens to use US government resources for his own petty ends, no matter how much damage he does to US interests by doing so:

He also made sure to inform the world that he is still seething about the statements a day later.
Meanwhile two US ambassadors to Ukraine resigned in a year because they can't stomach being complicit in Trump's nauseating "Russia First" policies.
In related news, Putin called Trump and told him to force Ukraine to not strike Russia during the May 9th celebrations (kind of a Russian equivalent to 4th of July). Trump claimed this was his idea, which is preposterous because Trump doesn't know that day is a holiday in Russia, let alone how important it is to the Russian state propaganda machine. The Russian readout (doubtlessly accurately) claims that this ceasefire idea was brought up by Putin.
These one day ceasefires at Russia's convenience are useless for Ukraine. During the last, 10,000 violations perpetrated by the Russians were recorded by the Ukrainian side.
Their point is to help the Russian government avoid the embarrassment of air raid alarms during their many parades on that holiday, and to allow the Russia armed forces to resupply and rotate their front line troops.
This is why this is not negotiated between Russia and Ukraine, but given as an order to Trump for him to enforce by leveraging the resources of the US government to support Russia, which he has always been happy to do whenever he gets to hear his beloved Putin's voice.