The jihadist group, in other words, is effectively a neighbor of the Jewish state — but it’s not the one that most concerns Israeli leaders. That would be Assad’s ally Hezbollah and its backer, Iran. Donald Trump has argued that defeating Isis should be America’s overwhelming priority in Syria. When the U.S. president arrives Monday in Israel, he’ll likely be urged to take a different view of the conflict — and maybe to help protect Israel from its fallout.

Islamic State “is being decimated,” said Avi Dichter, chairman of the Israeli parliament’s Foreign Affairs and Defense Committee, and a former head of the Shin Bet internal security agency. “They no longer have that many men on the ground. Iran, on the other hand, is a major regional threat.”

If that threat is present in Syria and directed at Israel, he said, “that’s a casus belli.” Israel fought a month-long war in Lebanon with Hezbollah, a Shiite Muslim militia armed and supported by Iran, a decade ago.