Israel’s killing this week of six Hezbollah fighters and a top Iranian general in a helicopter raid in Syria is the latest and boldest attack by the Jewish state against the Shia party in recent years. Hezbollah has vowed to retaliate, and many of its supporters, urging the party to respond swiftly and forcefully, have advised Israel to “prepare its shelters.” If the three-decade history of confrontation between Israel and Hezbollah is any guide, the latter is likely to strike back to protect its credibility. But that is not inevitable. The Syrian conflict has transformed Hezbollah, arguably turning it into a more cautious foe of the Jewish state.

Hezbollah is a survivor. Since its formation in the early 1980s, the Shia party has made it through three high-intensity military conflicts with Israel, the assassination of several of its top leaders, the departure of its Syrian patron from Lebanon in 2005, and significant political crises in Beirut. Power, money, and performance, chiefly enabled by Iran and Syria, have allowed Hezbollah to become the dominant group in Lebanon and a key player in the high politics of the Middle East.

But the Syrian civil war is challenging Hezbollah’s domestic and regional position. If Syrian President Bashar al-Assad’s regime falls, Hezbollah would lose a key supporter from a country that historically has played a dominant role in Lebanese politics. Even more important, Syria is Iran’s closest ally, and Tehran was calling in its chits by asking Hezbollah to close ranks around the Assad regime. Should Syria fall, Hezbollah could lose a storage facility and transit route for weapons from Iran and Syria to Lebanon. But should Assad leave, or his jihadist opponents grow stronger, the gravest threat Hezbollah (and Lebanon as a whole) would have to imminently deal with is Sunni extremism as represented by groups such as the Islamic State of Iraq and al-Sham (ISIS). Sunni radicals would not settle for controlling Syria. They would also seek to expand into Lebanon to go after their number one bogeyman, Hezbollah. Already, Sunni jihadists have struck Hezbollah targets and the Iranian embassy in Lebanon, among other places.

By intervening in Syria to come to Assad’s aid, Hezbollah’s chief Hassan Nasrallah has put his party on a collision course with Syria’s (and many of the region’s) Sunnis—moderate and extremist alike. Indeed, despite Hezbollah’s military advances in Syria, Sunni militants have been able to penetrate deep into the Shia party’s sphere of influence and wreak havoc. More important, the same extremists that Nasrallah was hoping to fight outside Lebanon could turn Lebanon into another Iraq, a country defined by Sunni-Shia sectarian violence. Another Lebanese civil war would be a major distraction from the military struggle against Israel.

Hezbollah also risks military setbacks. Hezbollah has beaten back Israel’s military from Lebanon, earning it healthy respect from Israeli military leaders, something conspicuously lacking for other Arab military forces. At any given moment, there are perhaps 5,000 Hezbollah soldiers in Syria, but Hezbollah regularly rotates its forces to limit the impact. Even so, the strain is showing. Because of its heavy role in Syria, Hezbollah is more militarily invested in Iran than ever before. In Syria, the Islamic Revolutionary Guard Corps’ Quds Force assisted Hezbollah with command-and-control and training. Entering the war was in part payback for past favors, but the move tied Hezbollah even more tightly to its Iranian master. Finally, Hezbollah believes that it has a military role in Lebanon because of Syria. Along the border, its forces cooperate quietly with the Lebanese Armed Forces, patrolling and even laying mines to prevent infiltration.

Hezbollah is both battle weary and battle hardened. The Syria experience has bloodied its forces, making them more skilled and allowing Hezbollah to test its commanders. At the same time, the heavy death toll and the constant strain are overwhelming, and Hezbollah could not easily take on a new foe. The fighting in Syria is also different from fighting Israel: Hezbollah is, in essence, a counterinsurgency force, taking on less-organized, poorly trained, and lightly-armed rebels. The Israel Defense Forces are a different, and far more dangerous, kettle of fish.

As a result, Hezbollah’s military threat to Israel is uncertain. The growing range of Hezbollah’s rockets puts all of Israel in danger, although the success of the “Iron Dome” missile defense system offers Israelis some comfort. Nevertheless, Hezbollah is in no mood for an all-out war with Israel. The memories of the disastrous 2006 conflict are still fresh, and the drain of the Syrian conflict makes Hezbollah even more cautious. Although Israel likewise has no interest in a broad fight, conflict might break out depending on how Hezbollah chooses to respond to Israel’s latest deadly assault.

Despite Hezbollah’s role in terrorism, the United States and Hezbollah currently share many interests—a reality both sides hate and would deny. Yet both are at war with ISIS, and both want to prop up Iraqi Prime Minister Haidar Abadi’s government in Baghdad. Even within Lebanon, although Washington supports Hezbollah’s weak political rivals, it recognizes that Hezbollah is helping hold the country together and that an ISIS expansion or a descent into chaos would be a nightmare.

A slight shift could turn suspicion into conflict. U.S. military actions in Syria are focused on ISIS and thus are indirectly helping the Assad regime, Hezbollah’s ally. Yet if Washington decides to live up to its anti-Assad rhetoric and take on the Syrian regime as well as ISIS, it will also be taking on Hezbollah. Similarly, Hezbollah is more in bed with Iran now than ever before, and any military action against Tehran over its nuclear program must factor in the Hezbollah response.

Hezbollah remains a potent regional actor: a stalking horse for Iran, and a prop to the Syrian regime. Nevertheless, the organization is also overtaxed militarily and on the defensive politically. Therefore, as painful as the loss it has just suffered is, it wouldn’t be shocking if Hezbollah decided to hold fire, or at least limit its response.

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  • BILAL Y. SAAB is Senior Fellow for Middle East Security at the Brent Scowcroft Center on International Security at the Atlantic Council. DANIEL BYMAN is a Professor in the Security Studies Program at the Edmund A. Walsh School of Foreign Service at Georgetown University and a Senior Fellow at the Center for Middle East Policy at the Brookings Institution. Follow him on Twitter @dbyman.
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