Dream on. The recovery of Truman's reputation and regard had a bit more to do with just the eventual reconsideration of the Korean War. To that end, Bush's ill-repute goes much further than his regretful decision to invade Iraq.
As an example, read the following excerpt from a Truman speech, replace "communism" with "terrorism" and try to imagine Bush saying any of it.
There is a right way and a wrong way to fight communism. This administration is doing it the right way, and the sensible way.See the difference? Any questions?
Our attack on communism is embodied in a positive, threefold program:
One, we are strengthening our own defenses and siding free nations in other parts of the world so that we and they can effectively resist Communist aggression.
Two, we are working to improve our democracy so as to give further proof, both to our own citizens and to people in other parts of the world, that democracy is the best system of government that men have yet devised.
Three, we are working quietly but effectively, without headlines or hysteria, against Communist subversion in this country wherever it appears, and we are doing this within the framework of the democratic liberties we cherish.
That is the way this administration is fighting communism. That is the way it is going to continue to fight communism. Now I am going to tell you how we are not going to fight communism. We are not going to transform our fine FBI into a Gestapo secret police. That is what some people would like to do. We are not going to try to control what our people read and say and think. We are not going to turn the United States into a right-wing totalitarian country in order to deal with a left-wing totalitarian threat.
In short, we are not going to end democracy. We are going to keep the Bill of Rights on the books. We are going to keep those ancient, hard-earned liberties which you lawyers have done so much to preserve and protect.
After reading this it should be no shocker to understand why Truman's standing has risen over the years. On the contrary, given the abominations, the screw-ups, the purposeful ruin wrought, the spreading of hate and fear for political gain, the disregard and destruction of our Constitution -- just a few of many things beyond the Iraq War, it should likewise shock no one that Bush will not experience a similar recuperation in standing. It's absolutely inconceivable and with good reason.