GWEN IFILL: Now we return to the root of what's forced millions from their homes: the conflict in Syria.

With multiple factions and common enemies in play, the war has become even more complicated, as Russia now steps up its support for Syrian President Bashar al-Assad by moving additional military men and weaponry into Syria and expanding its base there.

Meanwhile, Moscow is calling for greater coordination with the U.S. to fight a common enemy: the Islamic State group.

Joining me now to help us sort through some of this latest tangle is chief foreign affairs correspondent Margaret Warner.

So, Margaret, where does this proposal or this talk about having joint U.S.-Russia talks stand tonight?

MARGARET WARNER: Well, Gwen, even though there's been no official announcement, in fact, you could say the military-to-military talks have ray begun.

Last Friday, Secretary of Defense Ash Carter had a conversation 50 minutes with his counterpart, and this had been 18 months in which the Obama administration had cut off all contacts after Russia seized Ukraine or certainly seized Crimea.

So the question they're trying to figure out, OK, publicly, they're saying, the U.S. is saying, well, these are deconfliction talks. Make sure that our planes don't interfere with each other and we don't have an accident.

That is part of it. But really what they want to know is, what is Assad's intention here? And is it to prop up the Assad government? I'm sorry — Russian's intentions are to prop up the Assad government, or in fact is it just to fight ISIS, which is what Kerry had been told by Lavrov?

GWEN IFILL: Now, is this just old Cold War suspension, or do we have reason to be worried that this is more than what Russia says it is?

MARGARET WARNER: Oh, well, that's exactly — and the administration will admit this — they do not want to be gamed, as several said to me, the way they were in Ukraine, where President Putin and Foreign Minister Lavrov, Sergei Lavrov, consistently, in the U.S. view, lied, not only to them on the phone, face to face, but lied to the world about whether they were in Ukraine and what they were doing in Ukraine.

And so this time, they didn't want to be sucked into that. They also want to make sure, you know, if his intention is to help Assad fight ISIS and they adopt Assad's view, which is everybody opposed to me is a terrorist, well, the U.S. doesn't want to get sucked into that kind of endeavor or that kind of partnership.

GWEN IFILL: I can understand that, but I just don't see — how do face-to-face talks mean that they will tell the truth or that they will get the truth?

MARGARET WARNER: Excellent point, Gwen, because Kerry has already had three conversations with Lavrov.

Based on what happened in Ukraine, there is no guarantee they will be told the truth. And the interventions with Lavrov on the phone have, so far, not slowed the Russian advance of weapons and materiel and men into Syria at all.

GWEN IFILL: Is there any worry or concern that part of the deal if Lavrov were to talk to Kerry or Putin would talk to president…

MARGARET WARNER: Again, which might happen next week.

GWEN IFILL: Which might happen next week in New York.

Is there any concern that the tradeoff might be keeping Assad in power?

MARGARET WARNER: Oh, yes.

And, in fact, in London just this weekend, Secretary Kerry said, well, essentially, that Assad could be part of the transition. Now, when you ask why the turnaround, administration officials tell me there is no turnaround. If you were at the Geneva Syria peace talks 18 months ago, as I was, or you read the clips, which I read again today, Kerry's tone was absolutely hard and fast. There is no role for President Assad even in this transition phase.

Yesterday or this weekend, Kerry said, well, we're not obdurate about that as to time and place.

GWEN IFILL: And why the change? So there was a change, but why?

MARGARET WARNER: Oh, there's definitely a change, because — for two reasons.

One, there is an urgency to get something going on the political process. And that's what Kerry is hoping, is that this invitation to talk about military-to-military will open up an opportunity and that we could cooperate with the Russians on that, as we did on Iran.

So, one, it's the E.U. The European migrant crisis is driving it, and, two, a growing concern that in fact Assad and everybody other than ISIS is losing control completely of Northern Syria, and that the thing is just getting completely out of hand.

GWEN IFILL: For the record, what is it that Russia says it is actually — they say that they're actually doing?

MARGARET WARNER: They say they are there — they have always had a base in Syria. This is not new. And they…

GWEN IFILL: Advisers, not military.

MARGARET WARNER: Well…

GWEN IFILL: Well, who knows.

MARGARET WARNER: I don't know. I don't know the details of that.

But this is totally different. The base is being expanded. There were reports by Reuters, which no one would confirm to me, that Russia is already flying surveillance drones over Syria. So what they want to make sure doesn't happen is that essentially Assad gets this tremendous help from the Russians and turns around and uses it against his own citizens, barrel-bombing them, as Assad is doing now.

GWEN IFILL: It sounds almost — and tell me if this is too simplistic — like a pool game, that, on one hand, the migrant crisis is pushing them toward Russia, but they're afraid that Russia may have a bank shot which takes them back toward Assad. Does that make any sense?

MARGARET WARNER: I couldn't have said it better. I couldn't have said it better. That's exactly it.

And, as you say, the track record is such that there's no reason for President Obama to believe President Putin anyway.

GWEN IFILL: So, who holds the cue, just following through on that?

MARGARET WARNER: I don't know. Probably Putin, as he manages to do.

Obviously, he's trying to get out of the deep freeze he's been in with the rest of the world over Ukraine. And the U.S. doesn't really want to be an enabler to that. At the same time, they want to learn more about the military operations.

So, the administration, it strikes me, is a little bit caught. And then you also always have Secretary Kerry, who, having completed the Iran deal, some people say may be just looking for another great negotiation he can get going.

GWEN IFILL: Well, there's plenty out there left to be done, but one last thing.

So, next week is the United Nations General Assembly. This is where any meeting between the president and President Putin would likely occur.

MARGARET WARNER: Yes.

GWEN IFILL: Where does that stand, an actual face-to-face of leaders?

MARGARET WARNER: There is still — there is debate and discussion in the White House over this, I'm told.

It is very much in the air. Kerry and Lavrov will obviously talk, probably extensively and several times, in a bilateral, just the two of them. So, I wouldn't be a bit surprised if Presidents Obama and Putin were to meet.

GWEN IFILL: And there will be a pool cue in the corner waiting.

MARGARET WARNER: Yes.

GWEN IFILL: … fix it up.

GWEN IFILL: Margaret Warner, thank you very much.

MARGARET WARNER: Thanks, Gwen.