Analyzing Islamic State’s military successes and failures thus far, Hillel Frisch notes that after its stunning victories in 2014 over the ill-trained and poorly motivated Iraqi army, IS has had trouble defeating the Syrian and Kurdish militaries, and would likely be at a far greater disadvantage against the IDF. True, there are reasons to fear IS will expand its control in Syria and from there into Lebanon and Jordan, giving it an opportunity to attack Israel. Nevertheless, Frisch concludes, the greater threat to Israel lies elsewhere:

[The significance] of an IS takeover in Syria to Israeli security interests is not so much the IS threat per se, but rather the Iranian reaction to the takeover, and the threat such a reaction would pose to Israel. Israel must meet the Iranian challenge [by establishing] clear red lines, the most important of which is the prevention of the transfer of advanced missile launchers and rockets through both seaports and airports in Lebanon and [a Syrian rump state outside of IS control]. Israel must develop the intelligence capabilities to monitor these facilities, if it has not already done so.

[Furthermore, Israel should] clearly signal to Iran that infringement of these red lines will result in the partial or complete destruction of the installations in question. . . . [It must also establish a] geographical red line in southern Lebanon beyond which an Iranian presence will not be tolerated.

Israel should [likewise] consider an IS assault on Jabal al-Druze, [an area of Syria bordering Jordan and near the Golan Heights] as a red line, automatically initiating a forceful Israeli response. . . . Israel should signal to the organization that it will forcefully oppose any IS attacks or subversion against Jordan [and that] any attack on Israel or Israeli citizens outside Israel, or any attempts to begin operations in Judea and Samaria, will meet with a disproportionate counterattack on IS personnel and infrastructure.

Surveying news websites and social media on Sunday morning, I immediately found some intelligent and well-informed observers arguing that Iran deliberately warned the U.S. of its pending assault on Israel, and calibrated it so that there would be few casualties and minimal destructiveness, thus hoping to avoid major retaliation. In other words, this massive barrage was a face-saving gesture by the ayatollahs. Others disagreed. Brian Carter and Frederick W. Kagan put the issue to rest:

The Iranian April 13 missile-drone attack on Israel was very likely intended to cause significant damage below the threshold that would trigger a massive Israeli response. The attack was designed to succeed, not to fail. The strike package was modeled on those the Russians have used repeatedly against Ukraine to great effect. The attack caused more limited damage than intended likely because the Iranians underestimated the tremendous advantages Israel has in defending against such strikes compared with Ukraine.

But that isn’t to say that Tehran achieved nothing:

The lessons that Iran will draw from this attack will allow it to build more successful strike packages in the future. The attack probably helped Iran identify the relative strengths and weaknesses of the Israeli air-defense system. Iran will likely also share the lessons it learned in this attack with Russia.

Iran’s ability to penetrate Israeli air defenses with even a small number of large ballistic missiles presents serious security concerns for Israel. The only Iranian missiles that got through hit an Israeli military base, limiting the damage, but a future strike in which several ballistic missiles penetrate Israeli air defenses and hit Tel Aviv or Haifa could cause significant civilian casualties and damage to civilian infrastructure, including ports and energy. . . . Israel and its partners should not emerge from this successful defense with any sense of complacency.