A Difference between Vietnam and Iraq
South Vietnam was unable to resist the invasion from North Vietnam largely because it was bankrupt. The official government of Iraq, in case you hadn't noticed, has some oil revenue.
Another Vietnam lesson to unlearn
I suspect many of the people anticipating “another Vietnam” figure that once the Americans leave, they're never coming back. They might have to unlearn that soon. We recently turned protecting Afghanistan over to NATO. If there's a Taliban resurgence and NATO wimps out, we're going back in. It looks like there's bipartisan support for that.
In view of the Islamist takeover of Somalia, we might be back in Somalia soon as well.
I'm sure the Iraqi insurgents will be taking notes.