My two cents:
War is never a straight line kind of operation. There are advances. There are pullbacks. There are periods of losing and periods of pressing forward to victory. In the Civil War it took three years of fighting with tens of thousands of casualties for the Union forces to turn the tide against the South's armies, and another 2 years of horrific battles to secure victory. Likewise, the losses sustained in the first several years of World War II were massive and intensely discouraging. One could easily have assessed by the end of 1942 that the Allied forces were not only losing against Germany and Japan but they could very well actually go down in defeat. In both of those wars, the Union forces and the United States military suffered grievous mistakes and defeats. But they were learning... the thing is that they became wiser from those mistakes, adjusted their strategies, redoubled their efforts and pushed on to victory.
In the same way, mistakes of strategy and force deployment have been made in the Iraq War. Fighting a non-uniformed enemy, not understanding their tactics, and not securing the safety of the population are part of the saga of the last three to four years. But our military has been learning and adjusting. And al Qaeda is on the defensive. The tide is turning.
From the Associated Press: as reported at ABC News... Analysis: Military Makes Gains in Iraq
From The New York Times: MICHAEL E. O’HANLON and KENNETH M. POLLACK longtime critics of the Iraq War have just returned from Iraq and in their article, A War We Just Might Win state "Here is the most important thing Americans need to understand: We are finally getting somewhere in Iraq, at least in military terms. As two analysts who have harshly criticized the Bush administration’s miserable handling of Iraq, we were surprised by the gains we saw and the potential to produce not necessarily “victory” but a sustainable stability that both we and the Iraqis could live with."
From The National Review: Michael Barone's article "Defeating Defeatism: Perceptions are starting to shift. Quoting the authors from the above article, “There is enough good happening on the battlefields of Iraq today that Congress should plan on sustaining the effort at least into 2008.”