After years of false starts, the United States has signed a landmark deal with the Taliban to end the war in Afghanistan. We traveled to the front lines of the war — and to the signing ceremony in Doha, Qatar — to investigate whether peace is actually possible.Guest: Mujib Mashal, senior correspondent for The New York Times in Afghanistan.For more information on today’s episode, visit nytimes.com/thedaily. Background reading: The agreement between Washington and the Taliban seemed to be an important first step in ending the war in Afghanistan. Then the violence started again.Zalmay Khalilzad, the Afghan-born American envoy and architect of the deal, seemed to have been handed an impossible and thankless assignment. Here’s how he pulled it off.