Just a year ago, Hezbollah was sitting pretty. Lebanon’s Party of God had consolidated its influence across the Arab world with a durable set of alliances. Its Axis of Resistance, formed with Iran, Syria and Hamas, had emerged as the most credible and authoritative force in Middle Eastern politics. Its central idea—to mobilize self-reliant communities around a frontal confrontation with Israel—seemed to be setting the region’s agenda.

But the Arab Spring changed the rules of the game that Hezbollah so masterfully played for the last two decades. Today, the party faces perhaps the biggest threats to the legitimacy it has worked so hard to cultivate among cadres, casual supporters and even the political opponents who have come to grudgingly respect the effectiveness of its leader, Hassan Nasrallah.

The first, and more short-term, challenge comes from Syria, where a tottering Assad regime could severely curtail Hezbollah’s military room for maneuver. The second, more enduring, issue is the Arab political renaissance underway, which could produce movements well positioned to steal Hezbollah’s anti-Israel thunder with a resistance program free from the party’s sectarian, militant baggage.

Hezbollah has a long history of facing adversity and somehow—against all odds—recovering. Its guerilla war forced Israel to withdraw from Lebanon in 2000. Then the murder of a popular former Prime Minister, Rafik Hariri, in 2005 put Hezbollah on the defensive (several party officials have been indicted in connection with the assassination). A popular uprising drove Syrian troops from Lebanon, depriving Hezbollah of its immediate protector. Attacked from many sides, Hezbollah assiduously worked its considerable base and at the same time used every possible means to deter its domestic enemies, from savvy politics to hardball street battles.

It fought Israel to a standstill in 2006, silencing its Arab critics in the process. Two years later, in a short battle, Hezbollah crushed its domestic Lebanese rivals and won a decisive share of the government. By last summer, Hezbollah commanded half the Lebanese parliament and boasted a powerful, reconfigured militia fully supported by Iran and Syria.

Many of Hezbollah’s opponents thought, even hoped, it could be undone by the international court pursuing Hariri’s killers. But the court plodded its way to indictments, exposing itself as inept and possibly corrupt in its reliance on tainted witnesses. Nasrallah, meanwhile, convinced all of his followers and even many of his enemies that the Special Tribunal for Lebanon was part of an Israeli and American plot and that Israel was responsible for Hariri’s killing. To insulate itself against any charges, the party toppled the government of Saad Hariri, the slain leader’s son, in January of this year and installed a Hezbollah-friendly prime minister.

So when four Hezbollah officials were indicted in the Hariri murder at the end of June, the announcement barely registered. The Lebanese government is unlikely to pursue the men, and it probably wouldn’t be able to catch them if it tried. In a confident speech after the indictments, Nasrallah warned that no one should expect Lebanon to cooperate with the arrest warrants against Hezbollah. The state would ignore the warrants, he said, and he ordered his followers not to be drawn into violent disputes with the half of the country that loathes Hezbollah. “There will be no civil war in Lebanon,” he said. The court, which has charged Hezbollah with killing Hariri, is an American and Israeli plot, Nasrallah repeated. Case closed, as far as his followers are concerned—and as far as any likelihood of Hezbollah members facing trial.

It turns out that a crumbling dictatorship in Syria is bedeviling Hezbollah far more than the Special Tribunal for Lebanon. Nasrallah has publicly embraced his patrons in Damascus at a time when Bashar al-Assad is engaged in a war against much of his own public. Islamists and secular nationalists—who normally sympathize with Hezbollah for its long record of fighting Israel—find themselves in Assad’s crosshairs, with Hezbollah’s full rhetorical support.

It’s not likely that Hezbollah would try to provoke an all-out regional war if Assad were about to fall, as Nicholas Noe recently argued in these spaces. Historically, Hezbollah has shrewdly embarked only on wars that will have the full support of its constituents. Lebanese will support a war against Israel that appears to be a question of national sovereignty or dignity; they would chafe at a war perceived to be engineered in the interest of a foreign regime, whether Syria’s or Iran’s.

It’s unclear whether change in Syria is an existential matter for Hezbollah; it’s quite possible that a successor to Assad might support resistance against Israel. But if Hezbollah continues to ally itself with Assad, rather than Syria’s popular will, it begins to look like a movement that prefers Arab tyrants to the Arab Spring.

This taint on Hezbollah’s hitherto impeccable credentials as an Islamist and national force speaks to the second, and greater, threat to the movement over the long term:

For the first time in recent memory, Hezbollah faces challenges to its legitimacy from other authentic Arab political forces, movements that also oppose Israel’s policies but do not support Hezbollah’s ideology and tactics.

In Egypt, for example, new political movements want to contest Israel by cutting off intelligence cooperation and natural gas sales, opening the border to Gaza and supporting Palestinian movements like Hamas. Such a policy might cause concern in Jerusalem and Washington, but it also offers the Arab world a path to resist Israel that falls far short of Hezbollah’s recipe of direct and perpetual militancy.

Until now, Hezbollah has remained popular throughout the region because of its resistance project, despite an authoritarian and Islamist internal culture that many outside the party’s immediate ambit find distasteful. In a vigorous marketplace of political ideas, Hezbollah’s share might shrink markedly.

Although Hezbollah is at a peak in terms of military and political power, it is fast coming under scrutiny for siding with repressive dictatorships in Iran and Syria even as the rest of the Arab world is engaged in cataclysmic political change. It will have a lot of explaining to do to its core activists and casual supporters about its choices at this historical moment. That conundrum, more than any other, could prove Hezbollah’s undoing.