Nerguizian: The rapid advance does have certain immediate implications, but they're not static or easy to determine. Right now, if you did not have stable Assad control over western Syria – and it is right now, it's a consolidated structure from Deraa up to Latakia with minor, symbolically important gains like this weekend's retaking of Kessab – you'd have a lot more concern within the Assad regime and their interest groups about what the ISIS offensive means.
ISIS is still useful in terms of making the case that terrorism is the byproduct of policies against the Assad regime – that ungoverned spaces have emerged, largely thanks to this idea that you can just conduct dramatic policy shifts in places like Syria and nothing will happen. So it does play in to the Assad regime's narrative that it's either them or the terrorists.
But at the same time you're going to keep seeing Assad benefit from an indirect relationship with these groups that are largely transactional. So irrespective of the intervention by ISIS more aggressively in Iraq, you're going to keep seeing Assad buying oil from fields controlled by ISIS [in eastern Syria]. ISIS has a similar view – for them, the focus is on consolidating the space between Syria and Iraq where the Assad regime doesn't have any immediate pressure to expand its control. They're not looking to take back Raqqa, they're not really looking to make a push into Deir Ezzor. They realize that maintaining effective control over the parts of Syria that matter to the regime are far more important. And ISIS knows this. ISIS in the short term is happy to ignore Assad for as long as possible.
If Assad really does consolidate his hold on the west up to Aleppo, and he feels that there's enough space and maneuverability that he can do more, there's always [pressure] to do that. This isn't something that would map out until the end of the year.
Syria Deeply: Is there any outside power that could now step in and contain the ISIS state?
Riedel: The Maliki government is most likely to try and recover from Mosul, and that will require rebuilding an Iraqi army, which is not likely to happen overnight. There's really no outside power that wants to take on the challenge of getting rid of the ISIS emirate in the middle. Turkey is probably the one that's most capable – and closest by – but after three years of war in Syria, the Turks have made it clear that they don't want to get sucked into what they see as a quagmire.
Karasik: The only thing that's going to stop them is trying to wipe them out, and Maliki has said that the real action will have to be done by the U.S. and/or Iran. That could change what's happening in Syria, too, because if the U.S. and Iran are cooperating on Iraq, then maybe they can find some kind of common accommodation on Syria.
I'm sure a lot of the other [rebel] groups in Syria are watching ISIS's progress – including Jabhat al-Nusra, the Islamic Front and the Free Syrian Army. The groups on the ground that are against Assad's regime are going to see the success ISIS is having, and it might give them a spark to try and up their game a little bit and see how they can make progress.
Syria Deeply: How would involvement in Iraq impact Iran's support of the Syrian regime?