The death of Yahya Sinwar at Gaza is a moment to mark the success of Israel’s war against Hamas in the year since the assault of October 7. The only civilized response to the horrors of that day was to ensure that they would never be repeated. That is what Israel has been doing in the coastal enclave, and now in Lebanon. Sinwar, dispatched to his reward by the Israel Defense Forces, died for a death cult that is destined to lose. 

Sinwar has much blood on his hands, both that of Palestinian Arabs and Israelis. He was known to behead those he suspected of collaboration. He yielded nothing to Torquemada when it came to the techniques of torture. He was called “The Butcher of Khan Younis” and rose through the ranks of Hamas. Time in an Israeli prison was a turning point. He studied Hebrew, wrote a novel, and pickled in the brine of his hatred for Jews and their state. 

Exchanged, along with 1,000 other prisoners, for an IDF soldier, Gilad Shalit, Sinwar returned to Gaza a conquering hero. He went about preparing the territory for war, all while spewing promises of apocalypse and jihad. Those who imagined him reformed in intent or cautious in design were proven wrong. He bolstered Hamas’s ties with Tehran and laid the groundwork for the assault on southern Israel. Hiding in tunnels, he hoped to start a regional war.

Sinwar now shares the fate of the Hezbollah leader Hassan Nasrallah and such fellow travelers as Ismail Haniyeh, Fuad Shukr, Mohammed Deif, Marwan Issa, and Ibrahim Aqil, among others bent on the murder of Jews. Israel’s critics — including those in the Biden administration — argue that the destruction of Hamas was an impossibility. They pushed Jerusalem toward a ceasefire that would have left Sinwar free to pursue his cause.

There is a special irony in Sinwar being slain in the Tel al-Sultan area of Rafah. It was Rafah that was President Biden’s “red line.” In March, he blustered that if Israel went “into Rafah, I’m not supplying the weapons” and that “we’re walking away from Israel’s ability to wage war in those areas.” He called Israel’s intent to fight there “wrong.” Jerusalem evacuated more than a million civilians, pounded Hamas, and delivered to Sinwar his deserts.

With Sinwar gone we imagine that Washington will bear down even harder on Israel for a ceasefire. The plight of the hostages and their families is unbearable. Now, though, is also the time to keep up the fight against not only what is left of Hamas — whom Mr. Netanyahu a year ago called “Amalek” — but also Tehran. Sinwar’s death, after all, is another breach in the mullahs’ “ring of fire” that has emerged as the strategy set in motion by Iran to destroy Israel.

It would be fitting if along with Sinwar there also perished certain notions of how peace is secured in the Middle East. Mr. Biden’s penchant is for appeasement and de-escalation, exactly the wrong approach. Ms. Harris’s hostility to Mr. Netanyahu gained nothing. Newspaperman Thomas Friedman’s estimation that Israel was “spiraling” was followed by a run of intelligence and military successes rarely matched in the history of combat.

Mr. Netanyahu calls the end of Sinwar “the beginning of the day after Hamas.” He tells Gazans that “Sinwar ruined your life. He told you he was a lion, but in reality he was hiding in a dark den.” The premier promises immunity to anyone who releases hostages, but warns that “whoever harms our hostages, his blood will be on his head. We will come to a reckoning with him.” It is, one could say, a choice between a blessing and a curse.