Historian Robert Dallek describes the parallels between Iraq and Vietnam in this astute essay in the Washington Post. Here's a brief sample:
Like Johnson and Nixon, President Bush is hoping that adding troops will turn a civil war around, is relying on local, U.S.-trained forces to stave off defeat, and is worried that failure will undermine America's international credibility. Bush also disdains antiwar voices and is determined to prove them wrong in the long view of history. But unlike Johnson and Nixon, he doesn't seem to realize that his war is lost. Instead of learning from his predecessors, Bush seems to be replicating their mistakes.