When a United Nations tribunal began trying those accused of the 2005 assassination of Lebanon’s former prime minister, a prosecutor struggled to paint a portrait of the main suspect. “He has never been issued a passport or a driver’s license. He is not the registered owner of any property in Lebanon. The authorities have no records of him entering or leaving Lebanon,” the prosecutor said in January 2014 of the defendant, Mustafa Badreddine, who was being tried in absentia. “He passes as an unrecognizable and virtually untraceable ghost throughout Lebanon, leaving no footprint.” Last week, the Lebanese Shi’ite militia Hezbollah announced that Badreddine, its top military commander, had been killed in a “huge explosion” near the Syrian capital, Damascus. Badreddine is the most senior Hezbollah official to be killed since the group sent thousands of fighters to Syria in 2012 to help save the regime of President Bashar al-Assad. The support of Hezbollah and its main patron, Iran, has been crucial for Assad to remain in power since a 2011 popular uprising quickly turned into a civil war involving several regional and Western powers. Despite initial reports in the Lebanese media that Badreddine was killed by an Israeli airstrike, Hezbollah refrained from blaming Israel, its main enemy. On May 14, the day after Hezbollah announced Badreddine’s death, the party said its operative had been killed in an artillery attack by “takfiri groups,” a catchall term Hezbollah uses to describe jihadists like those of Islamic State and a range of other insurgents fighting the Syrian regime. Hezbollah said its commander’s “martyrdom would increase our determination to continue the fight against these criminal gangs, and to defeat them.” But no insurgent faction in Syria has claimed responsibility for killing Badreddine, and monitoring groups as well as residents of the Damascus suburb where Hezbollah says the attack took place dispute its account that there was shelling in the area. It’s possible that Hezbollah is deflecting blame on to Syrian rebel groups to avoid a new confrontation with Israel, which has assassinated more than a dozen senior Hezbollah leaders since the 1990s. Hezbollah would not want to risk a wider war with Israel right now, by retaliating for Badreddine’s death with a confrontation along the Lebanese-Israeli border. The group is already engaged in wars on two fronts: In Syria, where it is fighting rebels and jihadists, and in Lebanon, where it is trying to contain spillover attacks from groups like Islamic State. More broadly, Badreddine’s assassination underscores how vulnerable Hezbollah could become due to its deepening involvement in Syria, and its commitment to help Iran keep Assad in power. The group has lost 1,200 to 1,500 fighters in Syria, according to Lebanese officials. While Hezbollah remains the dominant military and political force in Lebanon, its Shi’ite supporters are paying the price for its role in the Syrian war, both by losing young men on the battlefield and in civilian casualties inflicted by sporadic bombings of Shi’ite areas in Lebanon. But even as it loses support in the wider Sunni world, Hezbollah has managed to keep its Shi’ite base intact. Under Lebanon’s sectarian political system, the Shi’ites have few alternatives to the Party of God. Hezbollah has always portrayed itself as a nationalist and pan-Islamic movement committed to fighting Israel. But Syria has turned into Hezbollah’s quagmire: many Sunnis view the group as complicit in Assad’s brutal crackdown against an insurgency led by Syria’s Sunni majority. Since it was founded in the 1980s, Hezbollah has received financial, military and political support from Iran. The Islamic Revolution’s leader, Ayatollah Ruhollah Khomeini, once hoped that the group would help export the revolution to the Arab world, but Hezbollah later abandoned the cause of creating an Islamic state in multi-confessional Lebanon. When Lebanon’s 15-year civil war ended in 1990, all of the country’s militias were disarmed. But Lebanese leaders allowed Hezbollah to keep its weapons as a “national resistance” against the Israeli occupation of southern Lebanon. After Hezbollah’s guerrilla war forced Israel to end its 18-year occupation in 2000, the militia was hailed throughout the Arab and Muslim worlds for achieving what no Arab army had done before: force Israel to relinquish land without a peace agreement. With the Israeli withdrawal, Hezbollah moved into the vacuum in southern Lebanon, opening clinics and schools, and providing small-business loans. The group also expanded its military capability, deploying thousands of missiles along the Lebanese-Israeli border. Many Lebanese wanted it to disarm and become a strictly political party, but Hezbollah’s leaders refused and have since gone to great lengths to protect their weapons. After it battled Israel to a draw during a month-long war in 2006, the group’s popularity soared once again throughout the Muslim world. But by early 2011, the party’s status began to wane after the U.N. tribunal indicted several Hezbollah members in the 2005 assassination of Rafik Hariri, Lebanon’s ex-prime minister and most prominent Sunni leader. (Badreddine was one of the five Hezbollah operatives indicted in Hariri’s killing, and prosecutors accused him of being the plot’s “overall controller.” The trial is ongoing at The Hague, and Hezbollah has denied responsibility.) In May 2013, Hezbollah’s leader, Sayyid Hassan Nasrallah, confirmed what everyone in Lebanon and Syria knew: that the Shi’ite group’s fighters were deeply involved in the Syrian civil war, fighting alongside Assad’s regime to regain territory lost to an assortment of Syrian rebels and foreign jihadists. Nasrallah went further, committing Lebanon’s most powerful militia to preserving Assad’s rule. “We will continue this road until the end, we will take responsibility and we will make all the sacrifices,” Nasrallah thundered, speaking via a broadcast link to a large rally of supporters. “We will be victorious.” Nasrallah’s speech was timed to the anniversary of Hezbollah’s greatest accomplishment: the withdrawal of Israeli troops from southern Lebanon in May 2000. He used that symbolic date to invoke Hezbollah’s history of “resistance,” framing the battle in Syria as part of his group’s broader struggle with Israel. “Syria is the back of the resistance, and the resistance cannot stand, arms folded, while its back is broken,” he said. Iran views Syria as its most important strategic ally in the Arab world, and it has committed tremendous resources to protect Assad’s regime. Syria is also a gateway for Iranian weapons to reach Hezbollah in Lebanon — the weapons Hezbollah’s leaders insist they need to protect Lebanon from Israel. After its long intervention in the Syrian war, fighting alongside the Assad regime, Hezbollah’s reputation has plunged once again. In the eyes of the wider Arab and Muslim worlds, it’s now another sectarian militia working to advance Iranian interests. And the death of a top commander pulls Hezbollah deeper into Syria’s quagmire. Mohamad Bazzi is a journalism professor at New York University and former Middle East bureau chief at Newsday. He is writing a book on the proxy wars between Saudi Arabia and Iran. He tweets @BazziNYU