towers were attacked. >> we will stay until the mission was done. >> reporter: the mission? to defeat al qaeda and kill its leader, osama bin laden, ultimately accomplished. driving out the taliban and building an afghan government that can stand on its own. >> we will stand with you as you defend your own democracy. >> reporter: it was a commitment lasting 20 years, costing the u.s. $2 trillion. >> americans' commitment to you and to a secure stable and unified afghanistan, that remains firm. >> afghans will secure and build their own nation and define their own future. >> we have trained and equipped a standing force of over 300,000 afghan personnel today. 600,000 troops deployed multiple times, working to train the afghan army. >> the bulk of the country