It is this ethno-religious solidarity, more than continuing support by the Pakistani state, that is providing the Afghan Taliban with their bases inside Pakistan. This support from large elements of the Pakistani population will continue as long as Western soldiers are present in Afghanistan. Their presence, as well as US drone strikes on targets in Pakistan, also helps legitimize the campaign of the Pakistani Taliban against the Pakistani state. Since the survival of that state is a US interest that vastly outweighs anything that might happen in Afghanistan, it follows that the US goal should be to reduce that presence as soon as this can be managed, not to follow a strategy that risks prolonging it indefinitely.
The main question, of course, will be how soon the White House and the Pentagon decide that it is time to talk to the Taliban. Victory on the battlefield is not possible but peace cannot be achieved without US participation in negotiations.
What makes the enterprise so difficult is that victory usually requires more than just defeating the insurgents in firefights. It usually demands nation building as well because it is essential to fix the political and social problems that caused the insurgency in the first place; otherwise, it is likely to spring back to life. So even if it was a sure bet that the United States could succeed at counterinsurgency with the right people and doctrine, it would still take many years to achieve decisive results.
Fact: In Helmand and Qandahar Provinces, a poll found that 92% of male residents had never heard of 9/11.