JUDY WOODRUFF: To explore why the security environment has deteriorated so much over the past year in Afghanistan, we turn to two people who've been intimately involved in formulating U.S. policy toward that country during the Obama administration.

David Sedney was deputy assistant secretary of defense for Afghanistan, Pakistan and Central Asia from 2009 to 2013. He's currently a senior associate at the Center for Strategic and International Studies. And Barnett Rubin was a senior adviser at the U.S. State Department from 2009 to 2013. He's now a senior fellow at New York University's Center on International Cooperation.

And we welcome you both.Barney Rubin, let me start with you.Why has the situation in Afghanistan, security situation, deteriorated so much in the past year?

BARNETT RUBIN, Former Defense Department official: I think that a more realistic question would be, why hasn't it deteriorated more?

Bear in mind that, a couple of years ago, there were, I think — David, correct me if these figures are wrong — 100,000 U.S. and maybe 30,000 or 40,000 other NATO troops in Afghanistan. And those are the best military forces in the world, with, as Defense Minister Stanekzai, was saying, the most up-to-date equipment and so on. And now they're down to, I think, 8,000 U.S. and about 4,000 European.

And each of those soldiers cost a million dollars a year. So we were spending over a hundred billion dollars a year. So, if you withdraw them from the battlefield, of course there's going to be a change in the security situation. But the fact is that, despite the withdrawal of that huge force, the Afghan government and the Afghan military, for all the problems they have, have held on extremely well, and have not lost any major population centers.

JUDY WOODRUFF: So, David Sedney, is it largely due to the drawdown of U.S. forces?

DAVID SEDNEY, Former Defense Department Official: It's partly due to the draw down. I agree with Barney on that.

The Afghan forces have done very well. But we built a large Afghan army. And the numbers are there. And the Afghans are willing to fight. The big problem is, is, we didn't put in the enablers that Defense Minister Stanekzai was talking about, air support, helicopters, intelligence. We ripped those out of Afghanistan before the Afghan forces were ready to operate on their own.

And we're now paying the price. But the causes go beyond that. The Taliban have mounted in the last two years, since we stopped fighting, we stopped using combat forces, their largest offensives ever. More Afghans are dying today than at any time since before 2001.

JUDY WOODRUFF: At the hands of the Taliban?

DAVID SEDNEY: At the hands of the Taliban. This offensive is enabled by sanctuaries in Pakistan. And it has also been enabled by an internecine struggle among different Taliban factions and with a new factor in Afghanistan, Da'esh, the Islamic State, which is seeking inroads there as well.

This adds all up to much more violence and many more deaths.

JUDY WOODRUFF: Barney Rubin, are these factors that the U.S. should have anticipated, or did they just pop on the scene, to everyone's surprise, particularly the Pakistan and the Da'esh, or ISIS, presence?

BARNETT RUBIN: Well, I mean, by the U.S., that would be David and me and our bosses.

And I think that we did anticipate it. And the fact is, we didn't — you know, the president decided that the national interest of the United States wasn't served by having our military, with all those resources, in Afghanistan for more than 15 years.

We understood that that would mean a deterioration of the military situation. And that means that it's more important than ever for us to move ahead with the diplomatic and political solution, and also with the investment in regional infrastructure which is just getting off the ground now.

Unfortunately, there were some people in our government who thought you could just postpone those things until the military option was successful. But, of course, that was never realistic. We're paying the price for that partly now, but, in fact, we still are moving in that direction.

And despite the serious deterioration, the increase in violence that David has talked about, again, bear in mind, possibly taking Sangin district, which you called strategic — I'm not sure why — in Helmand Province is a long way from taking Kabul or any major provincial center.

JUDY WOODRUFF: You mean because of the size and the location of it?

BARNETT RUBIN: Yes. The Taliban took over Khanashin District in Helmand. I'm not sure that any government ever controlled Khanashin District. It's mostly empty.

JUDY WOODRUFF: David Sedney, what about the other argument we sometimes hear that prolonging the presence of large numbers of U.S. forces in that part of the world, it basically embolden — it makes the other side, whether it's the Taliban or ISIS, want to fight the U.S. even more?

DAVID SEDNEY: Well, the last two years have proved that wrong.

In fact, as we have withdrawn, as Barney said — we had over 140,000 U.S. and other countries' forces there two-plus years ago — we barely have 10,000 there now. As those forces have reduced, the Taliban offensive has increased. The Taliban use of violence has increased as foreign forces have decreased.

So it's not the question of presence of foreign forces. It's a question of control and power. The Taliban have made clear they want to rule Afghanistan. When the Taliban have taken more territory this year — and they have — they have gone out and killed civil society people. They have persecuted women. They have gone back to exactly the same kind of things that they were doing before 2001 that made Afghanistan such a hellish place to live for most Afghans.

JUDY WOODRUFF: So, Barnett Rubin, that being the case, what can the U.S., what can the Afghan government do to counter that?

BARNETT RUBIN: Well, we are — first of all, again, to come back to David's most important point, this is not just a conflict between the Taliban and the Afghan government.

It's a regional conflict, and particularly the basic source of it is the conflict between Afghanistan and the state of Pakistan. The Taliban wouldn't be able to mount all these offensives and so on, though they would exist and they would have to be dealt with politically, if they didn't have undisturbed sanctuaries in Pakistan.

And the reasons for that, other than Pakistan being evil or terrorist-supporting, Pakistan has certain interests in the region. And we are now trying to address those diplomatically. It's extremely difficulty. We have to have enough forces on the ground in Afghanistan, so that the situation remains relatively stable to give us the space to do that diplomatic work.

We're now getting much more support in that work from China and so on. So, I think that the focus that the media have on the back and forth of controlling 100 meters there and 100 meters somewhere else in different remote parts of the country is missing the point.

The main weakness on the Afghanistan government side is not whether their forces can fight the Taliban. It's the political divisions within the Afghan government which sometimes undermine the forces. And on the other side, the main issue is that the Taliban's sanctuary in Pakistan, not how strong or angry they are.

JUDY WOODRUFF: David Sedney, how do you see what the U.S. and others need to do to turn this around?

DAVID SEDNEY: I agree that the eventual aim is peace. And, ideally, that would be peace talks with the Taliban. But, in the meantime, the Taliban offensive has to be stopped.

German Defense Minister de Maiziere, when she was in Afghanistan last week, acknowledged that the NATO-U.S. withdrawal had been too hasty and ill-prepared and pledged that Germany would increase by over 15 percent its troops in Afghanistan.

Just today, Turkish Prime Minister Erdogan, meeting with President Ghani, pledged that Turkey would keep its military presence and work for peace through strength. We need to reverse the mistakes we made in the past and give the Afghans the help that Defense Minister Stanekzai asked for earlier in your program.

Otherwise, people will die well before peace talks have a chance to start.

JUDY WOODRUFF: So, if 5,500 troops into 2017 is not enough, what is the right number?

DAVID SEDNEY: There's no real right number. It's right capabilities.

We don't need combat troops there. We need the enablers that Defense Minister Stanekzai asked for. The Afghans need air support, intelligence support, the logistics support and well-trained advisers. A few years ago, we disbanded the group that the Army had — the U.S. Army had created to train people on how to build other countries' armies.

So, we're now sending advisers to Afghanistan who just, unfortunately, don't know what they're doing. We need to give the Afghans the help they need. They're ready to fight. We don't need combat troops. But they do need our help.

JUDY WOODRUFF: We appreciate your perspective, both of you, at the end of this year.

David Sedney, Barnett Rubin, thank you.