HARI SREENIVASAN, PBS NEWSHOUR WEEKEND ANCHOR:

The war in Afghanistan is now the longest in American history. It's been almost 17 years since the United States invaded in retaliation for the September 11th terrorist attacks carried out by al Qaeda, the terrorist group harbored at the time by the Taliban-led government.

To date, 2,396 American military personnel, along with 1,136 coalition soldiers have died in the war. So have an estimated 170- thousand fighters and civilians in Afghanistan and Pakistan.

Now, with the Taliban having regained control of 40 percent of the country, the Trump administration is contemplating a surge of 5,000 U.S. troops to add to the more than 8,000 still there.

Joining me here to discuss this is Barnett Rubin, associate director of New York University's Center on International Cooperation. He previously worked in the Obama State Department.

Thanks for joining us.

So, how do we get there? Why are we still 17 years out and we're talking about our adversary controlling 40 percent of the country?