Is the Taleban's success a surprise?

The Taleban are continuing their advance through Afghanistan, and are on the cusp of taking control in the major cities of Herat and Kandahar. The group's fighters have predictably ignored the Doha Agreement, but has the speed of their success taken politicians by surprise, and how much of an embarrassment is the deteriorating situation for the White House and Downing Street? Cindy Yu speaks to James Forsyth and Isabel Hardman.