According to Fareed Zakaria:
The most significant way we can help Iraq is to be there for the long haul, assisting it economically and politically, but maintaining a much smaller, more enduring military presence. That is a far more strategic role for U.S. troops than policing the streets of Baghdad. Making clear that we aren’t going to disappear entirely will change the calculus of all those groups in Iraq that are keeping their “post-American” options open.
Zakaria believes that sustaining the “surge” will detract from this overriding long-term purpose:
The president is wasting his limited political capital buying the surge a few more months. There is a much more important deal to be had here