As Barack Obama catches all manner of grief for failing to admit he was wrong about the surge in Iraq, it seems like a good time to examine the practice of admitting error in politics.

Is it necessary? Is it even a good idea? Is it something that used to be politically smart but is no longer in the current world of “gotcha” coverage?

Ultimately, it will be a case-by-case question. In the Obama instance, it is beyond doubt that his expectation of a surge failure turned out to be a very bad call.

But that’s not the bottom-line question. As even Obama supporters came to realize their guy was dead wrong about the surge, his campaign had to figure out whether it would be wise to admit it.

In real life, it’s easy. Admitting error is a cornerstone of any measure of good character. But in a presidential race, the far more pressing question is: Does it help the candidate win?

Could Mr. Obama have saved himself several waves of criticism if he had simply said, “Look, I’m still planning for a way to end this war, because I believe it was conceived wrongly and its focus is wrong. But did the surge work? Yes, and the people who planned it and the troops who made it work were right and I was wrong on that prediction.”

Sounds good, doesn’t it? So why won’t he say it? It’s not as though he has never wanted a do-over; just a few days ago, he recanted his quest for an undivided Jerusalem as the capital of Israel.

Critics instantly found evidence that he doesn’t mind slighting the troops or their commanders, but there’s no way he would offend Palestinians. There may be a nugget of truth to that, but I believe it goes deeper.

He says his request for a mulligan on the Jerusalem quote was nothing more than a “misspeak,” that common political foible now made into a clumsy noun. But a bad call on the surge is an actual lapse in policy judgment, the kind opponents can use to argue that similar lapses may lie ahead.

On balance, Mr. Obama should have owned up to his mistake and called it a lesson learned. When the media culture that adores him actually had to press him on this, the evidence was clear that admitting error would have been the way to go, as it usually is when one is running for president.

But what of those who have the job already, especially in wartime? Does admitting mistakes boost your stock or invite an endless litany of badgering?

A hostile press dogged President Bush for years when the war was not going well. They ridiculously wanted him to concede that the entire war was a mistake, which he will never do.

Unlike the Obama blown call on the surge, the war itself is debatable. Agree with it or not, the Bush position is clear, and events on the ground are beginning to justify his commitment.

But it has not been an effort without error. Even staunch war supporters can be found to fault the Rumsfeld strategy of 2003. “Shock and awe” actually had neither effect.

Could Mr. Bush have admitted at some point that we should have gone in with more troops and more firepower? Sure. But again, that pesky question: Would that have been smart?

Not in the ocean where he swims, filled with press corps sharks who would sniff for the next perceived “error” to pester him over, serving their agenda of making the war seem futile and unwinnable.

So, across party lines, it may be that candidates, whose main goal is to be broadly liked, should admit to obvious errors. But presidents, whose main goal is to lead even through press and public disapproval, should save such introspection for their memoirs.

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