JUDY WOODRUFF: On Israel's border, a morbid anniversary passes this week for a raging war which has claimed more than 200,000 lives, and has left millions homeless.

Four years in, and there's no end in sight to the killing in Syria. Just today, new government airstrikes hit a suburb of Damascus. And Syrian President Bashar al-Assad insisted again he's staying until his own countrymen decide otherwise.

PRESIDENT BASHAR AL-ASSAD, Syria (through interpreter): Whether they say I remain or not, the Syrian people have the final say on this particular matter. Anything that came from outside the borders was only words and interference that disappears after a while.

JUDY WOODRUFF: That last was aimed at Secretary of State John Kerry. Sunday, on CBS, he suggested any effort toward a transition in Syria would include Assad after all.

JOHN KERRY, Secretary of State: I am convinced that, with the efforts of our allies and others, there will be increased pressure on Assad.

QUESTION: And you would be willing to negotiate with him?

JOHN KERRY: Well, we have to negotiate in the end.

JUDY WOODRUFF: Kerry's words raised eyebrows, but U.S. officials quickly insisted President Obama's policy has not changed from this in 2012:

PRESIDENT BARACK OBAMA: President al-Assad has lost legitimacy. He needs to step down.

JUDY WOODRUFF: The push to oust Assad began as peaceful protests in March 2011, amid the Arab spring. But the regime launched a brutal crackdown against demonstrators that have, in turn, triggered a violent uprising across the country. Moderate rebels initially made some headway, but were hurt by internal divisions and a lack of Western support, and the intrusion of extremist groups like the al-Nusra Front.

At the same time, Iran and Russia bolstered Damascus with weapons, money and expertise. And Iran's Lebanese ally, Hezbollah, sent thousands of fighters into Syria. Then, adding to the chaos, the Islamic State group seized large sections of Northern Syria last summer.

Outside the White House yesterday, hundreds of expatriate Syrians, and Syrian-Americans, appealed for new action.

HADI AL-BAHRA, Former President, Syrian National Coalition: We need to treat the root cause of extremism and terrorism in the area, which is dictatorship and Assad regime itself.

JUDY WOODRUFF: But two rounds of peace talks have already failed, and many of the protesters say it's crushing to watch helplessly.

HASNA KAZMOUZ, Syria: I always feel like, I hope it's a dream, I hope it's a dream. But — and I'm afraid even to come and connect with the people, because I don't want to see it, I don't want to think about its reality. But, unfortunately, it's a reality.

JUDY WOODRUFF: And for now, the reality is that much of Syria has been blasted to ruins, as the war enters its fifth year.

So, when, if ever, will this conflict finally end? And how it will happen?

We hear from former U.S. Ambassador to Syria and current senior fellow at the Middle East institute Robert Ford. Hisham Melhem, he's Washington bureau chief for the Al-Arabiya news channel, and an individual who has had extensive experience working with the Syrian opposition, Steve Heydemann. He's a vice president at the United States Institute of Peace.

Welcome, all of you, to the NewsHour.

Robert Ford, to you first. Where does this conflict stand today? Does either side or any side have the upper hand?

ROBERT FORD, Former U.S. Ambassador to Syria: It's a long, grueling war of attrition. Iran is sending in more forces.

Iran is sending in more arms. The opposition is receiving help from other outside states, and the war just grinds on. I don't see any end in sight, at least in the near term.

JUDY WOODRUFF: Hisham Melhem, do you agree?

HISHAM MELHEM, Al-Arabiya Television: Absolutely. This could grind on for a number of years, short of a decisive move on the part of the United States and its regional allies.

This could last for a long time, precisely because you don't have two opposing sides, as if we had in the American Civil War or in the Spanish Civil War in the 20th century. This is — it's becoming almost a war of all against all, as Thomas Hobbes used to say.

And that is why it is extremely difficult to allow it to continue like that, because this is going to touch the whole region. What happens in Syria is not going to stay in Syria. Syria is close to Southern Europe and Syria is not Afghanistan. And the five countries around Syria, all of them are friendly to the United States, and all of them are paying a tremendous price.

JUDY WOODRUFF: Steve Heydemann, what's your assessment?

STEVEN HEYDEMANN, United States Institute of Peace: I tend to share the view that we are locked into a war of attrition. I think we do have opportunities to try to shorten this conflict through much more active, much more proactive diplomatic efforts, in particular on the part of the United States.

And I think we have to recognize that in the absence of those efforts, we are likely to see the conflict unfold for many, many years to come. It was very important that Secretary Kerry really indicated that he felt it is a priority to reignite a diplomatic process to try and bring the Syrian conflict to a negotiated settlement.

The real question is whether the U.S. has a strategy to act on the priority that Secretary Kerry expressed. So far, we haven't seen that, but it is a very important priority.

JUDY WOODRUFF: Well, let me ask each one of you, starting with you, Ambassador Ford.

What would an outside diplomatic intervention look like at this point?

ROBERT FORD: Couple of things.

First, the key regional states on all sides, because there are many states pumping in weapons and money to the opposing side's government and opposition, those states are going to need to agree on sort of the broad outline of what a settlement should be.

And it actually — I say broad outline, but it may have to be a bit more detailed. We thought we had such an agreement in the summer of 2012, in June 2012, what then Secretary of State Hillary Clinton came to an agreement with the Russians, with Arab countries, with European countries, with the United Nations on what such a settlement should look like. But the countries were unable to agree at the Geneva conference.

So I think we have got to go back and make sure that everybody agrees on the international framework. And the second part — and nobody has been able to achieve this yet — is, there is going to have to be an agreement among the regional states that are pumping in the weaponry that they will sanction the sides that break the agreed international framework, so that there is a price for not paying attention to what the international community wants to see happen.

JUDY WOODRUFF: So, Steve Heydemann, does that sound like the right approach to try to break through the stalemate?

STEVEN HEYDEMANN: I think we should also focus on what some of the opportunities might be to try and revive a process right now.

There's indications that the internal support for the regime is eroding. We have seen very little success on the battlefield on the part of regime forces. We know that the proxy states, Russia in particular, which has been an active supporter of Iran, is beginning to show signs of fatigue in sustaining that relationship.

So, while I do agree that the general approach that Ambassador Ford spelled out is the correct one, I wouldn't underestimate the extent to which the time that has passed since the first Geneva process may in fact leave us in a stronger position to move forward on a negotiation track than we were in January 2014.

JUDY WOODRUFF: So, Hisham Melhem, who should be at the negotiating table? Who is negotiating with whom?

HISHAM MELHEM: Well, before I answer that directly, this is predicated on the United States playing a decisive leading role.

JUDY WOODRUFF: So, the U.S. has to be there?

HISHAM MELHEM: Absolutely the United States has to be there, and the United States has to push the regional powers that contributed to the mess in the first place, allowing armaments and volunteers to go to Syria unchecked, especially through the Turkey-Syrian border.

JUDY WOODRUFF: Right.

HISHAM MELHEM: What characterized American policy from the beginning was dithering, indecision, weakness, and confusion.

JUDY WOODRUFF: And you're saying that has to change.

HISHAM MELHEM: That has to change. The United States can still help the opposition, the non-jihadi opposition. OK?

Any group we can deal with, short of supporting al-Qaida or ISIS, and any group that is going to — even Islamists, if they are not going to impose Islamic Sharia by force, these people will be at the table. Remnants of the regime will be at the table. Even if Assad is at the table at the beginning, in the end, there has to be a clear American position, from the opposition, from the Arab side, and from Turkey that Assad will have no future in Syria.

Then we can talk about serious transition. But the United States has to put the parts together. There's no leadership so far, and that's part of the problem.

JUDY WOODRUFF: Ambassador Ford, does that sound like the way you get from here to some kind of a productive conversation?

ROBERT FORD: It's an element. It's not the only element.

There has to be a great deal more pressure on the Syrian government itself. Thirteen months ago in Geneva, when Secretary Kerry was there, big international conference, the Syrian regime point-blank refused to negotiate any kind of political deal, point-blank refused.

So there is going to have to be a lot more pressure on the Syrian government to get them not only to go to the table, but to actual negotiate and be prepared to make some compromises, which is why it's important, even as the United States and our friends confront, fight the Islamic State in Iraq, confront, fight the Islamic State in Syria, ignoring the root cause of the Islamic State problem in Syria, ignoring the brutality of the outside regime and ignoring the need to get to a negotiated deal actually will lead us nowhere.

JUDY WOODRUFF: Right.

And let me turn to Steve Heydemann, because many people are looking and saying who does the U.S. — who does anybody sit down with to represent the opposition anymore, because it's so fractured?

STEVEN HEYDEMANN: Well, there have been very, very interesting developments on the opposition side that, again, I think suggest some possibilities that the opposition, having taken far, far too long, wrapped up in internal struggles, is beginning to get its act together.

We have seen a couple of meetings take place in Cairo that have brought together a number of different factions within the opposition. The Russians, who are now more proactive on the diplomatic front than the United States is, has also brought together a number of different groups within the opposition, very limited, but nonetheless brought them together in Moscow with regime representatives to try to lay the foundations for what could be another round of a Geneva process.

JUDY WOODRUFF: Do you see something tangible happening in the next year?

HISHAM MELHEM: If the United States says, we're going to increase the training of the opposition, accelerate this process, and at the same time make it politically clear this man and his junta have no place in the future of Syria.

You have to give that clear message to the Syrians. And then you can appeal the non-jihadists to your case — to the cause, because there are jihadists who are going to be alienated, and we stand up with the United States and others and the regional powers. But then you have to work again on those moderate opposition, who will believe that Syria is a country that should maintain pluralism, that all the minorities will be respected, there will be no persecution, and all that.

This is the political element that the United States should push, and the United States actually has been pushing, but not very forcefully.

JUDY WOODRUFF: Well, as we enter the fifth year, a lot of that has not happened yet, and we look to see how it unfolds.

Hisham Melhem, Steve Heydemann, and Ambassador Robert Ford, gentlemen, thank you.