WILLIAM BRANGHAM:

So, will this cease-fire last, where so many others in the past have failed?

For that, I'm joined now via Skype from Tucson by Andrew Tabler, who's a fellow at the Washington Institute for Near East Policy, and Joshua Landis, who directs the Center for Middle East Studies at the University of Oklahoma.

Welcome to you both.

Joshua Landis, I would like to start with you first.

We have seen cease-fires come and we have seen cease-fires go. Are you at all confident that this one is going to last?

JOSHUA LANDIS, University of Oklahoma: No, I'm not confident. This is really not about the cease-fire holding. It's about Turkey being involved with Russia and Iran and essentially letting the rebels know that a new page has been turned, that Turkey cannot keep its — cannot keep its door open to the rebels, that it's closing the door, and that they're going to have to fend for themselves in negotiations with the Assad regime.