CSIS, 11 Sep 08: How Soon is Safe? Iraqi Force Development and Conditions-Based US Withdrawals
No one can be certain whether setting a timeframe for US withdrawals that ends in 2011 will lead to instability in Iraq, or that such a timeline will lead the US to hand over responsibility to Iraqi Security Forces before they are able to do the job. There also is nothing wrong with setting broad goals for withdrawing US forces from Iraq. The US wants to leave as soon as this is feasible, and at least since 2004, Iraq's Kurds have been the only group in Iraq that showed a consistent desire for the US to stay.

It also is impossible to be certain that the risks of early withdrawal will really be greater than the risks of trying to stay longer than Iraqi politics permit. There are good reasons to extend the US military and advisory presence at steadily diminishing levels until Iraq has developed security forces that are fully ready to take over key missions without US support, and Iraq has achieved a greater degree of stability.

It is at least possible that setting early timelines will force Iraqis to move towards political accommodation, to take hard decisions, and to develop security forces that are more effective. In fact, if all goes well in Iraq, deadlines like 2011 may prove practical – particularly if such deadlines do not preclude a large number of US military advisors. Moreover, the US ―occupation‖ is so controversial and unpopular that the cost of staying long enough to do every job right could be far higher in terms of Iraqi resentment and political backlash than the security benefits would be worth.

At the same time, it is not a good idea to bet a country -- and the outcome of a war -- on the strategic equivalent of filling an inside straight. Political rhetoric often makes such "bets on the outcome;" it also often loses the bet. Iraq still faces a large number of risks and problems where a US military presence does more to stabilize the situation than destabilize it, and where both Iraqi and US leaders will need to be careful and realistic about how quickly they can move......
Complete 166-page document at the link.