How might Iran retaliate for a U.S. drone strike that killed its most important general?
By attacking Israel.
A senior Iranian official has already threatened to strike Israel if America were to respond militarily to any Iranian retaliation for the death of Lieutenant General Qassem Soleimani, the chief of Iran's Islamic Revolutionary Guard Corps (IRGC) Quds Force, and the driving force behind Iran's network of proxy armies such as Hezbollah.
"If the US takes any action after our military response, we will level Tel Aviv and Haifa to the ground," said Mohsen Rezayee, Secretary of Iran's Expediency Council and a former IRGC commander, according to Iran's Fars News Agency. The council advises Supreme Leader Ali Khamenei, and also has legislative powers.
Ironically, that would be the sort of strategy employed by Iran's former number one enemy, Saddam Hussein. During Operation Desert Storm in 1991, Saddam fired 39 Scud ballistic missiles at Israel, in an attempt to provoke Israel into attacking Iraq and thus splitting the U.S.-led coalition of European and Arab states. The attempt nearly succeeded: Israel was barely dissuaded by U.S. pressure from retaliating.
Iran's rhetoric suggests that the main target of its ire is the U.S. But to borrow the language of the Bible, attacking Israel would offer Iran both a blessing and a curse. Tehran has a plethora of lethal options that could be employed against its arch-nemesis. Its proxy Hezbollah in Lebanon could conduct small ground raids into northern Israel, or even unleash some of its estimated 150,000 Iranian-supplied rockets (though at the risk of triggering a full-scale Israel-Lebanon war that could drag in Iran and perhaps the United States).
There is also Hamas in Gaza, no stranger to rocketing Israeli towns and which has recently reconciled with Iran after a split over the Syrian conflict. More important, there is Syria, which has become an Iranian firebase on Israel's border, with thousands of Iranian troops and advisers, plus a sizeable contingent of Hezbollah and other non-Syrian Shia troops propping up the Syrian regime. These forces can hit Israeli troops and settlements in the Golan Heights.
All of these methods offer two blessings from Iran's standpoint. First, they offer a chance to attack a key U.S. ally --- one in whom America has invested a considerable amount of prestige and resources – and thus embarrassing America without directly attacking America. Second, with Israel ringed by Iranian allies in Lebanon, Syria and Gaza, it's easy to strike Israel without employing Iranian forces on Iranian soil.
Nor does Israel appear eager to turn the Soleimani affair into war with Iran. Not that Israelis are sad about the demise of Soleimani, arguably their worst enemy, who has sponsored anti-Israeli groups such as Hamas and Palestinian Islamic Jihad, as well as instigating terrorist attacks such as the bombing of the Jewish cultural center in Argentina in 1992. But the Israeli government has disclaimed any involvement in Soleimani's death and made clear that it doesn't want to be dragged into the affair.
However, an Iranian-sponsored attack could also prove to be a curse. What if Israel does choose to treat an attack by an Iranian proxy as an attack by Iran itself? Prime Minister Benjamin Netanyahu has long threatened military action to stop Iran's nuclear program. An Iranian strike, even by proxy, could be the final straw, especially with Netanyahu under criminal investigation for corruption. While the U.S. has discouraged Israeli military action against Iran, the Trump administration may be more favorably inclined, if only to have someone else do the dirty work of confronting Tehran.
Israel's own security establishment currently rates the chances of an Iranian attack as low, even as a top Israeli think tank warns that the probability of an Israel-Iran war is high. Either way, modern Middle Eastern history is replete with miscalculations and misperceptions: Hezbollah leader Hassan Nasrallah had admitted that he didn't expect his group's ambush of an Israeli patrol to have triggered the 2006 Israel-Lebanon war.
So far, the Israel-Iran cold war has been a shadowy struggle waged by Iranian proxies, the Israeli Air Force, and the Mossad. Like the Americans and Soviets during the Great Cold War, both antagonists have more or less managed to avoid direct conflict with each other.
Iran does not want a war with America, which it might not lose but certainly would not win. Israel just might be an adequate substitute to suffer Tehran's wrath.