Operation Big Swinging Dick

Throwing another 20,000 troops into Iraq should be called "Operation Big Swinging Dick" -- because that's whose idea it was, and that's what the idea is.
It's a typical Dick Cheney balls-up, and the purpose is really just to show the Democrats and the GOP doubters that Bush is still the boss.
If you want to understand Iraq, read Juan Cole and Today in Iraq for the details and Steve Gilliard for the big picture. Here is Gilliard's summary of what has gone wrong for the Americans in Iraq:

. . . here's a brief explaination of why the Iraq war failed.
1)Iraq is not an artificial state, but one with distinct interest groups. Saddam spent much of his time protecting himself from, and catering to them. Some people, the Talibanis, the Sadrs, were never happy, but others were. If you try to fracture Iraq, no state will be strong enough to survive.
2) Exiles sold their fantasies of being conquering heroes and instead were met with contempt from the survivors of Saddam. They were weaker compared to the prevailing forces, the Sunni shieks, B'aathists, Sadrists and Sistani. All would define what would happen in Iraq far more than any exile.
3) There were two different plans for Iraq, both doomed to fail. The first was to hand the country over to Chalabi, which would have resulted in anarchy within days, or to establish a colonial regime. Since the infighting was so intense, neither plan was fully hatched until Viceroy Bremer was sent to bring order.
4)The Bush Administration had no respect for the complications of establishing order in a colony, so they sent the young and untrained to run Iraq. Few ever saw what they were supposed to be changing. The Americans neither trusted nor respected the Iraqis they were supposed to serve. Having no training in foreign service matters, they were more hinderance than help.
5)Combat never stopped. The US was unable to ever establish order in the streets of Baghdad, which meant their word was useless. Soon, those who worked with the Americans became targets. The Iraqis had a much better sense of how to manipulate the Americans than vice versa.
6) Despite all their blather, few people realized what this war was quickly turning into. They talked about Al Qaeda and dead enders, but in less than a year, the Shia were running major attacks on them. Only Sistani's intervention prevented a full scale war on the Americans. The US was falling into the trap of fighting a colonial war, while all the warbloggers talked about Islamofascism. While they were attacking Cindy Sheehan, they forgot one thing: her son was killed by the Sadrists. Which went against the narrative we had been fed.
7) By the time the Iraqis finally had elections, what you had was all the factions, excluding the Sunnis, in parliment, and they wanted revenge. The government forces quickly fell under the spell of various militias and while we trained them, they didn't improve their effectiveness. But the Mahdi Army did. SCIRI did, the guerrillas in Anbar Province did.
While there was a great deal of rhetoric about a united Iraq, the US was playing the game of divide and conquer. Their trump move was to install Hakim's puppet over Maliki. Until Sistani said no, and left the power in the hands of Sadr. The exact opposite of their plans.
It wasn't bungled execution.
No Iraqi government not controlled by the Sadrists could have survived. Because they are the majority. They had no interest in sharing anything or a democratic government. Because this is a colonial war, and no structure set up by the US would have had any credibility.

So 20,000 troops aren't going to make any difference at all. Apparently the Iraqi government is saying it will bring in Kurdish pesh merga units to disarm the militias - oh, sure -- while the Americans troops fight the Sunnis. Gilliard describes what is actually going to happen next:

. . . someone better realize that the Saddam execution and the Sistani quashing of the coup means the last man standing is the guy with the funny teeth and black turban.
Bush is so clueless and desperate that he doesn't realize he's being coopted into assisting ethnic cleansing. At the end of this, Sadr will be in near total control of most of Iraq's population.
Petraeus should know better. While US troops are getting killed killing Sunnis, Sadr will increase his control over the military and police. He thinks they're going to disarm the Mahdi Army? Hell no. The Mahdi Army are the real protectors of the Shia population, they have won support on the ground by saving lives and feeding people. The government is subordinate to Sadr and his supporters, and Sistani made that happen.
Bush and his supporters live in a cloud cuckoo land where they don't understand how they have been manuvered into this mess. Americans troops are being asked to die to establish a Shia theocracy in Iraq.