Killing another country’s civilian is not casus belli, especially when considering both countries are allied.
These terms are steeped in legal precedent and tradition. You may not agree them, or respect them, but that alone doesn’t change how they’re defined.
But that also doesn’t change the fact that this should be a serious diplomatic row with serious bilateral consequences, but so should have untold numbers of other war crimes committed against the Palestinians in general, and more specifically, against countless American citizens within the occupation zones.
Also, I’m pretty sure Joe isn’t cognizant about much lately, and I would wager that he only appears lucid when talking about events that happened 50 years ago.