The comparison was obviously designed to convey the disastrous consequences that followed our precipitous exit from Vietnam, something not always mentioned during the stock "Iraq is like Vietnam" debates. In context with Iraq it would probably be magnified, since this war is about direct national security threats, not hypothetical domino theories, etc. He clearly also wanted to convey the notion that 50,000 troops died in vain during that war, something he plans to avoid if possible during this one. If making that point is desperate it's only because the stakes are so high.
As to Warner, his comments must be taken in context. Right wingers are quick to dismiss and lefties only focus on the "withdrawal" statement, but in reality his thinking is quite Bushian:
“There are no parallels really," the Virginia Republican said. "It’s a different type of situation .. we were in a country (Vietnam) that really did not pose a threat to the internal security of the United States as these conflicts in Iraq and Afghanistan do.”A far cry from "we've lost". He understands the consequences of withdrawal but is trying to find a way to get the Iraqis to act. He also knows the Democrats will use the war as a political boat anchor to hang around the GOP's neck next year, something Bush doesn't have to worry about.
For Warner, that’s exactly the dilemma: He wants a withdrawal of 5,000 by Christmas — but he implies that a failed state in Iraq would pose a menace to the United States.
The bottom line for average Americans is fallout, not politics. We've got a stake in this outcome. As Warner said, there is no comparison between security threats. That said, allowing a perceptive win for terrorism by surrendering in Iraq simply cannot stand, no how, no way, and Americans need to push their elected officials hard to make sure it doesn't happen.
A must-read on this subject.