Victor Davis Hanson:

Americans have regularly changed their minds in the midst of their ongoing wars — and not just once, but often. War is a volatile enterprise. Tactics, strategies, and commanders must be sorted out amid death and destruction before the proper combination is found to defeat the enemy. In the meantime, the reasons for going to war, the manner in which the war is fought, and the objectives for which it is waged are constantly being weighed at home against the costs of conducting it. As a result, impatient democracies — and Americans are nothing if not impatient — are liable to suffer alternating fits of unrestrained optimism and utter despair.

This volatility has certainly characterized our current engagement in Iraq, but it has been no less true before. In the early days of the Civil War, a confident North was sure of quick victory in a righteous cause. After the slaughters of 1862 at Shiloh, Antietam, and Fredericksburg, the North then fell into collective querulousness and despair. By the summer of 1863, the North was ebullient again as its armies won crushing, near-simultaneous victories at both Gettysburg and Vicksburg. A year later, after the Wilderness, Spotsylvania, and Cold Harbor, Lincoln and all he stood for were reviled. Stalemate or concession seemed imminent — until General Philip Sheridan ran wild in the Shenandoah Valley and William Tecumseh Sherman took Atlanta on September 2, 1864.

…In the Korean War, to take another example, Seoul changed hands four times. Harry Truman, who had won support for the deployment of American troops in the summer of 1950 and then lost it with the massive Chinese invasion of December, left office in January 1953 with a 22-percent approval rating. But his successor Dwight Eisenhower, without materially changing American strategy or war aims, mustered fresh support for stabilizing the situation once General Matthew Ridgway had succeeded in restoring an autonomous South Korea below the 38th parallel, and in preventing further Communist aggression.