Vietnam: a costly, unpopular, "unwinnable" war that foments unrest at home and anti-Americanism abroad.
We "lost" Vietnam, not because we couldn't win it but because we weren't willing to bear the cost of winning it. The "loss" of Vietnam posed no obvious threat to America's vital interests. In that respect, the critics of the Vietnam War were right -- and I was one of those critics.
Some proponents of the Vietnam War predicted that our withdrawal from Vietnam would, in the long run, threaten America's vital interests by showing our potential enemies that we could be made to back down by the sight (or prospect) of body bags. As we saw in Lebanon, the Gulf War, Somalia, and Clinton's tepid response to terrorist acts, those proponents of the Vietnam War were right.
We are now engaged in a war against terror that we invited, in part, by our actions in Vietnam, Lebanon, and the rest. We are now engaged in a war to stabilize the Middle East, where America does, indeed, have vital interests.
Iraq: a winnable war in which America shows its willingness to protect its vital interests, despite much anti-Americanism at home and abroad.