I've argued we could succeed with the change in strategy and could succeed with few or no new troops.
Austin Bay notes the importance of the change in military strategy and the far more important non-military measures (though he does not argue against the extra troops, I should add, he does mention that whether you go in with a heavy footprint or a light footprint, each has advantages and disadvantages. It isn't the clear choice between the right and wrong approaches that troop level critics insist on):
What Petraeus has changed is the "level of presence" in violent areas. The relentless targeting of Shia and Sunni extremist organizations is a far more important feature of what Iraqis are calling "the new security plan" than simply sending more U.S. troops into the streets.
Since Petraeus took charge, the economic and governmental (Iraqi political) "lines of operation" have received increased public emphasis. This new emphasis is very much a part of the "surge." The "surge" is commonly referred to as if it were solely a fighting strategy -- in reality, the intent is to work synergistically with economic and political activities, and it amounts to armed nation-building. Iraq's provincial reconstruction teams (PRTs) are being revamped. Prime Minister Nouri al-Maliki's national reconciliation program remains the key Iraqi political endeavor. In Iraq, economic and governmental progress is a frustratingly incremental and painstaking effort, but that holds true for every other hard corner of the planet.
Last summer, I recognized that we should consider the heavy footprint approach in Baghdad even as we tried to work with a light footprint elsewhere in the Sunni center. This is what we are now doing in the central region of Baghdad and the surrounding areas. And whether it is a heavy or a light footprint, the objective is the same--to buy time with the military for the non-military lines of operations to advance sufficiently to dry up the insurgency and terrorism.
My worry about the troop surge is that the extra forces reduce our patience--our real need--to such a degree that the surge of troops negates the gains made possible by more troops.
We are on the right path to victory. I just don't know how long that journey is.