A 12-year war?

Defense Secretary Donald H. Rumsfeld, meanwhile, said it may take as long as 12 years to defeat the insurgents. He said Iraq's security forces will have to finish the job because American and foreign troops will have left the country by then. ... Rumsfeld said he is bracing for even more violence. "We're not going to win against the insurgency. The Iraqi people are going to win against the insurgency. That insurgency could go on for any number of years. Insurgencies tend to go on five, six, eight, 10, 12 years," Rumsfeld told "Fox News Sunday." [Emphasis courtesy of DailyKos]

What is the probability that the US will be able to train Iraqis to fight on their own? An e-history of the collapse of the South Vietnamese government in 1975 blames a number of purely military problems, but also mentions:

The ability of the North Vietnamese to wage a revolutionary war, which purported to offer the chance for a change in the political order as it existed, was extremely effective in mobilizing the population in the South to support its war effort. By contrast, the South Vietnamese government's inability to offer its people a similar change through the ideals of democracy and economic growth insured a lack of support for the Thieu government, especially during the crisis days of early 1975. The people and soldiers simply had no reason to fight for a government which failed to meet their needs. It matters little that the North's government was just as corrupt and more repressive, as evidenced by the conditions existing in Vietnam today; it matters only that the North Vietnamese and PRG were more effective in offering the people a definite change in the political order as it existed in South Vietnam in 1975.

Because Thieu could not effectively eliminate corruption within his regime, the enticing, ideological arguments offered by the North Vietnamese were able to drive a divisive wedge between the people of South Vietnam and their government. In summary, I intend to show that the collapse of the RVNAF had not occurred suddenly in 1975, nor was the collapse due to any one single factor. Instead, the reasons were many: low morale, uncontrolled corruption, incompetent leadership, and the cutoff of U.S. military aid and air support. However, unless the government of South Vietnam could solve its own political problems, it was condemned to, not only losing the support of its own people, but the support of the American public and Congress as well. The Vietnam War was for the South Vietnamese to win. However, the U.S. could only provide aid to buy time for the government of South Vietnam to make significant reforms and rally the support of its own people to win the war against North Vietnam.

One can argue that the current government of Iraq has no need to "change the political order" as it's supposed to be an improvement on the political order in the first place. The fact that, yes there are many civilian targets of the insurgents in Iraq, but the US troops occupying the country are by far the main target for them, means that the current government of Iraq has a long, long way to go to be self-sustaining. As the insurgents are already self-sustaining in the absence of any clearly visible outside support and in the absence of a unifying political figure, the US-supported government of Iraq has to play catch-up. Is there any serious reason to believe that it wil last any longer than Thieu's government did after the North Vietnamese offensive of 1975 began?

It doesn't seem as though a 12-year struggle is in the cards, with or without American troops occupying Iraq for that whole period. America's support for the war is rapidly drying up and it doesn't appear likely that a self-sustaining government can be created under any circumstances, with any amount of material support.