I don't know if yesterday was the most I've ever been embarrassed by an American leader; I'm still not letting W. off the hook for destroying Iraq. Biden continuing to suck up to Netanyahu in the midst of a genocide when Netanyahu was clearly doing everything he could to motherfuck the Democrats and bring back Trump was pretty pitiful, especially when it continued AFTER the election.
But in terms of public conduct? He either deliberately ambushed Zelenskyy so he could look tough on TV and dramatically cancel U.S. aid, or he managed to blow up a deal (a terrible one for Ukraine) because he needed his ego to be massaged. And while #1 is tempting because looking for a "rational" explanation is comforting...he did cast himself as a great dealmaker who could end the war.