JUDY WOODRUFF:

Wars in Afghanistan, Syria, and Iraq, tensions within the Gulf states, and a new administration trying to manage an exploding region, all topics for retired General David Petraeus.

He commanded American and coalition forces in the wars in Iraq and Afghanistan, and served as overall commander of U.S. military operations in the Middle East. He later served as director of the CIA in 2011 and 2012. He's now with a global investment firm.

We spoke a short time ago.

And I started by asking him about reports that the Trump administration will soon send 4,000 additional U.S. troops to Afghanistan, and whether he thinks it is a smart move.

GEN. DAVID PETRAEUS (RET.), Former Commander, Multi-National Force Iraq: I think it is, and it's heartening.

I think what we need to get to in Afghanistan is a sustainable, measuring the expenditure of blood and treasure, a sustainable, sustained commitment. We need to recognize that we went there for a reason and we stayed for a reason, to ensure that Afghanistan is not once again a sanctuary for al-Qaida or other transnational extremists, the way it was when the 9/11 attacks were planned there.

That's why we need to stay. We also have a very useful platform there for the regional counterterrorist effort. And, of course, we have greatly reduced the capabilities of al-Qaida's senior leaders in that region, including, of course, taking out Osama bin Laden.

But this is a generational struggle. This is not something that is going to be won in a few years. We're not going to take a hill, plant a flag, go home to a victory parade. And we need to be there for the long haul, but in a way that is, again, sustainable.

We have been in Korea for 65-plus years because there is an important national interest for that. We were in Europe for a very long period of time, still there, of course, and actually with a renewed emphasis now, given Russia's aggressive actions.

And I think that's the way we need to approach this. Now, to be sure, the forces …

(CROSSTALK)