Joe Biden arrives in Israel on Wednesday on a high-stakes visit overshadowed by catastrophe even before Air Force One touched down at Tel Aviv’s Ben Gurion airport. Eleven days after the Hamas attack that killed at least 1,400 Israelis, the US president faced the already tricky task of providing solace to a grief-stricken nation while attempting to persuade its leaders to prevent humanitarian crisis and even regional conflict. But that delicate mission became infinitely more complicated on Tuesday when an explosion at the al-Ahli Arabi Baptist hospital in Gaza killed hundreds of Palestinians sheltering from Israel’s bombing campaign. Hamas blamed...