Assad has used Hezbollah and Iran's Shia foreign legion as shock troops to spearhead offensives so his own shaky forces can hold what is cleared by the shock troops.
Hezbollah has already shown signs of strain in carrying out this role.
Assad's troops are showing signs that they can't even carry out the less demanding role of "hold" without stiffening by the foreign fighters.
Now the Iranian legion is apparently getting tired of being the shock troops:
Iranian Revolutionary Guard troops fighting on behalf of the Bashar al-Assad regime have reportedly withdrawn from a number of battlefronts and redeployed to strategic points around the Syrian capital.
“The Iranian leadership has withdrawn [IRGC fighters] because there is no strategic advantage for the forces in many areas and they have suffered heavy losses,” Italian Adnkronos news agency (AKI) reported Tuesday.
“The IRGC has now based itself firmly [around] Damascus,” sources close to Hezbollah told AKI.
Unless Putin decides to send in Russian troops to stiffen Assad's forces--perhaps as a Plan B to simply have Assad hold a rump Alawite state friendly to Russia (and Iran)--just who stops the rebels?
(As an aside, I was close to predicting the Islamic State in that rump Syria post, as I pondered what might happen if Assad did officially abandon large tracts of Syria:
I find it hard to believe Iraq would want more Sunni Arabs, but would Anbar Province secede from Iraq if they could join with Sunni Syrians and declare their own state?
ISIL declared just such a state, no?)
I still bet that Assad's forces crack first.
Even if it is a good idea to support Assad in order to fight ISIL in Syria, I don't think Assad can hold up his end of such a deal.
UPDATE: Strategypage has a good related post.
UPDATE: This article notes the strains on Assad's supporters and wonders if he will need to retreat to a core Syria to survive.
Note that even this Syrian army success north of Jordan takes place at a far southern location that is beyond the capacity of Assad's tired forces to hold if Assad retreats to a smaller realm to survive.