Thank God for Wayne Barrett and Dan Collins. In “Grand Illusion: The Untold Story of Rudy Giuliani and 9/11” (HarperCollins, 390 pages, $25.95) Messrs. Barrett and Collins make it known to the world that if Mayor Giuliani had spent all his time between taking office in 1994 and seeing the twin towers fall in 2001 preparing for the precise attack that came to pass, the emergency response on that faithful day in September might have been … slightly better.

If only there’d been somebody diligent on the New York City political scene throughout the 1990s — someone unafraid to take on the powerful — who could have steered the mayor in the right direction.

Alas, there was just such a brave soul all along: Mr. Barrett, tireless investigative reporter and Captain Ahab to Mr. Giuliani’s Moby Dick. And what did Mr. Barrett have to say on the pressing issue of international terrorism and its clear-as-day, imminent threat to the twin towers during those seven-plus years? Not a peep.

In Mr. Barrett’s 2001 book attacking Mr. Giuliani’s mayoralty, “Rudy!: An Investigative Biography,” terrorism hardly warranted a single mention — except to criticize Mr. Giuliani’s deployment of “an astonishingly excessive 37,000 cops citywide” during the terrorist-targeted millennium celebrations as “a chance to briefly insinuate himself into the subconscious of tens of millions of Americans.”

Perhaps this is all a bit unfair. But in the face of a book-length spewing of bile so unrelentingly hostile and unbalanced, fairness may be beside the point. Mr. Barrett and his co-author are clearly perturbed that Mr. Giuliani’s performance on September 11, 2001, may propel him to the presidency, so they have written a brief for any person who may hope to slow his march to the White House.

Messrs. Barrett and Collins are not telling an “untold story” at all. The major failings of New York City’s response on September 11 are well-known: from the disastrous siting of the Office of Emergency Management “bunker” in 7 World Trade Center, to the turf wars between the NYPD and the FDNY, to the tragic problems with emergency responders’ radios, which almost certainly led to the unnecessary loss of firefighters’ lives when they didn’t receive orders to evacuate.

These were all failings for which Mr. Giuliani and his administration can reasonably be held to account. But to paint them as a disclosure or an indictment of the mayor’s capacity to lead is a serious misreading of what Americans responded to when they saw Mr. Giuliani literally rise from the ashes — inspiring New York City and America with the confidence that the nation could do the same.

Americans weren’t in awe of “America’s Mayor” because he saw the terrorist threat before others did. While he had Yasser Arafat thrown out of a Lincoln Center function in 1995 (a beautiful gesture), set up an emergency management bunker (poorly placed as it was), and managed plenty of high-profile and high-security events (such as the millennium eve that Mr. Barrett considered such a hoot), Mr. Giuliani was no more a prophet than anyone else devastated and shocked by September 11.

Americans were in awe because Mr. Giuliani took charge in a situation that no one — including the mayor himself — had adequately prepared for. Messrs. Barrett and Collins allow that in the aftermath of that terrible day, Mr. Giuliani “invariably struck the right tone,” such as when he responded, after being asked about the number of casualties expected: “The number of casualties will be more than any of us could bear.” Yet, they dismiss all that as no more than political theater — something that masks the real story.

But the words, the images, the comforting of a bereaved city and nation when the president failed to step up to the plate for days — those are the real story of Rudy Giuliani and September 11. The job of a leader isn’t to be a seer. It’s to put a confusing and dangerous — and, yes, to the general public, frightening — world in context. And sometimes to do it on the fly. To project an image of strength. To project a sense of hope and resolve.

There are criticisms to be made of Mr. Giuliani’s style as a leader. He’s pugnacious, which can be quite a good thing, but which can also lead to petty fights. He’s obsessed with being in control, which can be inefficient, but which can come in pretty handy in the really tight spots.

But “Grand Illusion” isn’t the book that will allow Americans to evaluate any of these traits. Unceasingly hostile and utterly unconcerned with balance, it’s nothing but a Swift Boat ad in hardcover.

If journalists indeed write the first draft of history, these two leave their readers eagerly anticipating the second.

Mr. Sager is author of “The Elephant in the Room: Evangelicals, Libertarians, and the Battle To Control the Republican Party,” available from Wiley. He last wrote for these pages about political rhetoric.