Actually, I agree with what Bush did in Afghanistan. I just wish he had doubled down and cleaned out the country... then left.
"Nation building" in Afghanistan is a waste of time. They will always fight among themselves and about the only thing that unifies them is fighting an invader.
We should have withdrawn as soon as we cleaned out Al Queda and warned: if we have to come back again, we won't leave anything standing next time.
Iraq isn't much different: they fight among themselves, until someone invades. But, Al Queda wasn't hiding there. We should have just left them alone. If they wanted to get rid of Saddam, they could do it on their own.
The only "nation-building" that should have been imposed on Afghanistan should have been to break it into separate countries that encompassed as much as possible one major tribe each. Afghanistan is a creation by the bureaucratic, divide-and-conquer, mandarins of the British Empire and was designed from the very beginning to be unstable.
When I look at the tribal map of Afghanistan below I see at lease 6 countries: Small and isolated tribal pockets should have been offered relocation assistance.
You cannot build a nation out of tribes that have been at each other's throats for thousands of years unless you are willing to murder, enslave, and terrorize them and rule with an iron fist. I don't want to do that to anyone and I am sure that no parent wants to send their boys over to enforce that kind of rule.
The tribal Pashtuns, Tajiks, Hazaras, Uzbeks etc. deserve to keep their own identities and be in charge of their own destinies.
The discord and war that we are seeing in Afghanistan is a symptom of the disease of globalism and its desire to control everything by divide and conquer. 
Iraq isn't much different: they fight among themselves, until someone invades. But, Al Queda wasn't hiding there. We should have just left them alone. The founding leader of the organization known today as "ISIS," Zarqawi, was sitting in Baghdad with a bunch of his mostly Palestinian followers in 2002, a year before we invaded. At the time he had long commanded a smuggling route from Pakistan through Iran to Iraq and from Iraq to Syria and on to Italy. That he had not [yet] formally advertised that he was sworn to serve bin Laden was a technicality of little import since his terrorist organization had a long relationship with bin Laden even by that time and had already been involved in efforts to attack Americans in the Millennium plot of late 1999.