BEIRUT – The Assad family's grip on Syria has never looked so tenuous.

After 17 months of violence and an estimated 17,000 people killed, a lightning-quick turnaround in the momentum of the civil war has put President Bashar Assad's forces on the defensive, a sign that his once-impenetrable family dynasty is wobbling.

For the first time, the rebels have brought a sustained fight to Damascus, the seat of Assad's power, in a powerful signal that the regime cannot protect its own capital. On Friday, reports of intense fighting in Aleppo, Syria's second city, suggest the rebels are making a run on another major government stronghold.