If at first you don't succeed "try, try again." This can be a nice motto for many endeavors in life, but it shouldn't be for wars, no matter what John McCainsays.
When Kerry ran for prez. in 2004 he arguedthat he would send more troops, that he wouldn't try to win "war on the cheap," and since then, others of those critical of the Bush administration's handling of the war have made similar arguments that the problem with the war is that we haven't sent in enough troops to win the war. Many in the general population, even those against the war, will say the same thing. Just last night I was talking to a bartender in Windsor Terrace (hardly a lefty neighborhood) who was as critical of US foreign policy as anyone I've met in recent years. He was going on about the US's support of the Saudis and the Shah, and talked about his hatred for the whole Bush family. And he asked me, "in one or two sentences, how do we fix the problem in Iraq?"
My answer began, "first, pull the troops out." He objected strongly and said, "the root of this whole thing is the Sunni Shia conflict," and suggested that if the troops were to come out now, Iraq would be overtaken in chaos and civil war.
I almost replied that the "send in more troops" solution hadn't' worked in Vietnam and it wouldn't work here either, until I remembered that there's a whole popular school of thoughtthat the reason that we lost the war in Vietnam was that we fought it with "one hand tied behind our back."
My students always say on the first few days of class that they think history is important because if you don't know about the past, you'll be doomed to repeat past mistakes, but I beg to differ. It's not complete ignorance about the past, but the knowledge of useful mythologies about the past that allows people to confidently reapply wrong-headed strategies in the present day.
We need people like George McGovern, with all his incapacity to win elections, to remind us that "more troops" didn't work then, and it won't work now. The US occupation is the reason for the insurgency, so if the troops are pulled out, much of the energy and support for the insurgency will disappear, making it much easier for the Iraqis to quell any remaining "sectarian violence."
If your jury's out on what the insurgency is, and what is driving it, I recommend the following reading: Christian Parenti's The Freedom and Loretta Napoleoni's Insurgent Iraq.