Much of the history of the United States in the last half century has involved wars that the country should not have waged and from which it could not extricate itself.
In Korea the United States mistakenly decided to take on China after America had won a great military victory in the legendary landing at Inchon. If the United States had ended the war when it drove the communists out of South Korea, American casualties would have been light and the communists humiliated. Unfortunately, General MacArthur made the terrible mistake of assuming that China could accept an American army on its Yalu River boundary.
Hence one can generalize that mistaken wars will end only after there is a change of administrations. Korea was Harry Truman's war, Vietnam was Lyndon Johnson's war, and the Iraq war is George W. Bush's war. Only when the president who started the war leaves can this country manage to end the war which was identified with a previous president.
President Eisenhower promised that if elected he would go to Korea, though that promise was hardly enough to persuade the Chinese army to go home. President Nixon had a "plan" to end the Vietnam war, though in fact he did not. Although he and Henry Kissinger messed around in search for a dignified withdrawal and caused more U.S. casualties, he (and President Ford) could finally end the war that Johnson could not end. It is clear today Bush cannot (which means will not) end this most foolish of the three wars.
Why is it so difficult to extricate U.S. troops from an impossible situation?
The commander in chief was in each case personally responsible for the decision. Moreover, to rally support for the decision that in retrospect was a serious mistake (underestimating the enemy in each case), the president had to rally the national will with appeals to patriotism, honor and American self-interest. His emotional involvement in "victory" increased as the casualties did -- and in the case of Johnson and Bush some kind of identification with Abraham Lincoln took place. Finally, the president's political party resisted the temptation for a long time to criticize him.
Moreover, a substantial segment of the American public, especially Southern and Evangelical, believe that patriotism demands that the nation emerge clearly victorious no matter what the price. These people wave flags, talk about the threat to the United States (of a much weaker enemy) and accept the patriotic appeal that we simply don't lose wars and we must stand by our troops.
When they are told that we will not defeat the enemy because we cannot, they scream defeatism, surrender, betrayal. They also suggest that we should nuke the enemy. The pathological super patriots always fall back on the power of nuclear weapons to obliterate the enemy. Those who argue for withdrawal from an impossible situation are accused of cowardice and infidelity to our fallen heroes. A substantial segment of the officer corps of the military -- mostly out of harm's way -- become furious, though they were the ones who provided the advice on which the war was based.
It would seem, sadly, that we have learned nothing since the Inchon landing. A successful imperialist power (which the United States is not, cannot and should not ever be) has to be able to override a public turn against the conflict. Nor does the myth of American power, which is indeed great but not invincible, especially against peasant guerrillas, cause the leadership -- military and political -- to consider carefully all the risks of charging off to an easy victory against weaker opponents.
Indeed those, like Messrs. Bush and Cheney and Rumsfeld, who ignore the lessons of history are doomed to repeat its mistakes.
A war will probably not end when the party whose war it is loses a congressional election. That is not likely to happen in November anyway because the fear/patriotism/betrayal campaign will keep Republicans in control of Congress.