At the beginning of the Syrian civil war, many of Bashar Assad’s longtime allies were wary of openly supporting a discredited dictator who was slaughtering his own people. Hamas, which had long maintained a headquarters in Damascus, quietly sulked out of town. Hezbollah, which is tied by an umbilical cord of supplies to Damascus, kept its distance too. But with the Assad regime showing signs of hanging on after more than two years of combat, Hezbollah, and its patrons in Iran, have been more open in their support for the regime. Hundreds of Hezbollah fighters are now fighting alongside Syrian troops in the critical battle for the town of Qusayr near the major city of Homs. Dozens of “martyrs” are coming home to Lebanon in body bags.

By thus raising the stakes in Syria, Hezbollah is leaving itself open to serious blowback. Its credibility in Lebanon has always depended on its posture as an anti-Israel force; its prestige soared when it chased the IDF out of southern Lebanon in 2000 and when it stood up to Israeli attacks in 2006. But now in Syria, Hezbollah fighters are battling not the “accursed” Jews but fellow Muslims who are determined to rid their country of an unelected and unpopular leader.

Hezbollah is thus suffering a loss of credibility and prestige, especially among the Sunni majority in the Arab world which sympathizes with the largely Sunni Syrian insurgency battling against a minority Alawite regime. Hezbollah is seen not as a pan-Arab army but as a sectarian, pro-Shiite force. That is a vulnerability that the U.S. and its allies should exploit to try to loosen Hezbollah’s death grip on Lebanese politics.

In this regard it would help enormously if Hezbollah were not successful in its efforts to keep the Assad regime in power. A failed intervention in Syria would do tremendous damage to its standing in Lebanon, while a successful intervention would allow it to maintain its grip on power by safeguarding the arms pipeline flowing from Tehran via Damascus.

That makes it all the more imperative that the U.S. do more to ensure that Hezbollah loses in Syria–not only by providing arms to vetted rebel factions but also by employing our airpower to ground Assad’s air force and thus removing a crucial regime advantage. Time is slipping away as Assad recovers on the battlefield. If we don’t act now, the Tehran-Damascus-Bekaa axis (the Bekaa Valley is the birthplace of Hezbollah) could emerge stronger than ever.