The most difficult trait for a leader is to be reliably right ex post. Any idiot can be right ex ante. After all, all the relevant data is at least knowable. That so many are so wrong ex ante just demonstrates what fundamentally stupid and irrational creatures we really are.
But being right ex post is genuinely hard. The most important facts -- what's going to happen between the decision and the result -- can't be known. From the point of view of the future, every decision is a gamble and in this game not even the true odds are known.
It is, therefore, remarkable that President Bush is right as often as he is. I'm thinking here, in particular, of his decision on funding research into embryonic stem cells. Given what we've discovered since, his decision that the federal government would fund primarily research into adult stem cells turned out to be the right decision scientifically. The world doesn't usually work like that: morality doesn't necessarily translate into doing what best from a purely utilitarian view point. Not torturing terrorists is the right decision, but pretending that there's no cost in the form of dead Americans because "torture doesn't work" is simply ignoring the cost of our decision.
A president who makes decisions that turn out for the best in the long run is invaluable. It might also be unknowable until the person actually becomes president. There was, for example, no way to know that Jimmy Carter would be the anti-W, a president who's every important decision turned out to be wrong. This does show, though, that democracy has no special talent for being right ex post.