It's unfair to compare the results of a full censorship/multimillion dollar propaganda regime like the US in WWII with either Vietnam or Iraq.
Why Johnson, Nixon, and President Bush all decided not to use the war power of the United States to sustain their policies, as Roosevelt, Wilson, and Lincoln had done before them, is a mystery to me.
The war power of the United States is virtually without limit. If it were exercised today, cable channels would be broadcasting good news from the war zone 24/7, Michael Moore and Kos would be in detention facilities, AND you could have your posters.
As appealing as that sounds, I'm happier this way...