The U.S. President says the country had specific goals in Afghanistan that it achieved long ago. Therefore, there is no need to leave the troops there now.

“We went to Afghanistan almost 20 years ago with clear goals: get those who attacked us on September 11, 2001 - and make sure al Qaeda could not use Afghanistan as a base from which to attack us again.
We did that - a decade ago.
Our mission was never supposed to be nation building”, - writes Joe Biden.