What in the world happened to Rudy Giuliani? How did the man whose bravery and resilience reassured a nation during the 2001 terrorist attacks become a bellowing, cheek-stained geyser of nonsense?

Andrew Kirtzman sets out to answer that question in “Giuliani: The Rise and Tragic Fall of America’s Mayor.” Kirtzman is well-suited to the task; as a New York-based reporter he covered Giuliani for years and was alongside the mayor on 9/11 as he sought to rally a devastated country.

Giuliani’s image as a national hero was set in stone that day, but the former mayor, prosecutor and presidential candidate has spent the years since chipping away at the pedestal on which he stands, largely through truth-twisting diatribes in defense of Donald Trump. Kirtzman’s biography attempts to explain how a man who nobly defended the country in one of its darkest moments then devoted his twilight years to sabotaging it.

It’s a measure of how much Giuliani’s place in history has changed that this is Kirtzman’s second biography of him. The author argues that it’s not so much that Giuliani changed as age, alcohol and a thirst for attention gradually led his worst impulses to dominate his life. Giuliani’s self-confidence, Kirtzman writes, “drove his greatest crusades, from his mission to eradicate the mob, to his determination to clean up New York City. . . . But the almost fanatical sense of righteousness that propelled his rise also presaged his catastrophic fall.”

It can be difficult in 2022 to recall Giuliani’s remarkable early career, when he became mayor of a city that many considered in 1994 not just dangerous and dirty, but out of control and fundamentally unmanageable.

Giuliani hurled his obsessive, combative and vindictive spirit into taming New York. Crime plummeted, corporate profits soared, and three-card monte dealers in Times Square gave way to Disney characters.

As mayor, he found an ally in Trump the real estate developer, but their relationship went far beyond any zoning regulation or fundraiser; the two men were in some ways kindred spirits, people whose careers were boosted and shaped by New York’s unique tabloid news culture. Rudy and the Donald thrived in a public discourse dominated by personal feuds and peccadillos.

After 9/11, the respect and admiration for Giuliani swelled so high, people often burst into spontaneous applause when they saw him in public. That public love translated into tremendous wealth and political influence, and Kirtzman details the years in which Giuliani cashed in with a global business brand.

In 2007, “America’s Mayor” sought to trade the imaginary title for a real one by running for president. Starting with the best name recognition and donor pool in the GOP, Giuliani burned through both in record time, exiting the race in an Orlando hotel ballroom, having amassed a grand total of one convention delegate.

Giuliani spent the post-election period in a deep funk and, to hear his ex-wife Judith Nathan tell it, drinking too much. Giuliani and Nathan holed up at Trump’s Mar-a-Lago Club in Florida, using the complex’s tunnels to stay out of public view.

At times the book seems more interested in Giuliani’s troubled marriage than his estranged relationship with reality, but “the ex-wife made him do it” defense offered by some of Giuliani’s former advisers feels like a too-convenient excuse, since after the divorce he became even more closely tied to Trump.

“What’s clear is that the two men’s friendship survived when a hundred other Trump relationships died away like so many marriages of convenience,” Kirtzman writes. “Giuliani would never turn his back on Trump, much to his detriment.”

After the failed presidential bid, Giuliani’s legal and consulting career withered, as his increasingly strident political commentary turned off law partners. During the 2016 campaign, Giuliani rediscovered his public voice as a pro-Trump attack dog, going on Fox News to accuse Hillary Clinton of all manner of crimes and illness.

It was a testament to the collective memory of Giuliani as a hero in a crisis that the nonsensical accusations he made that year did little to dent his reputation. Even Kirtzman, in his deconstruction of the former mayor, seems to credit Giuliani’s claims to have sources inside the FBI in 2016 telling him about the Clinton investigations. When federal agents questioned Giuliani in 2018 about that – an interview in which lying could lead to criminal charges – he admitted he didn’t have any inside information.

In that interview, Giuliani conceded what should have long been obvious to the outside world: that he had made wild claims based on little to no evidence, on the belief that false accusations are an acceptable part of politics.

“You could throw a fake,” he told the agents.

Trump’s 2016 victory gave Giuliani sway with the most important person on the planet: the president of the United States. The same spaghetti-on-the-wall strategy Giuliani had deployed against Clinton he now aimed in the general direction of the Biden family, trying to build a case of corruption out of Ukraine, where Joe Biden’s son Hunter had business interests. Rather than get his client Trump reelected, Giuliani helped get him impeached.

And still, people believed.

In Tampa, 38-year-old crane operator Paul Hodgkins watched a televised news conference in late 2020 in which Giuliani claimed the election had been stolen from Trump. As Giuliani spoke, what appeared to be dark hair dye oozed down the side of his face. Hodgkins thought Giuliani was not someone who would make something up or “chase fairy tales.”

By then, Giuliani had been publicly chasing fairies and goblins for the better part of four years. But Hodgkins still believed in America’s Mayor, so he went to Washington on Jan. 6, 2021, took part in the pro-Trump riot and was sent to jail.

Kirtzman’s Giuliani is a tragic figure, one whose lack of fear spelled doom as he aged. Giuliani is now 78. The president is 79, the House speaker is 82, and Trump is 76. As our country’s leadership ages in place, the house of government may need more handrails.

What happened to Rudy Giuliani? The more pressing question posed by Kirtzman’s book is what happened to us, that it took so long to see it.

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Devlin Barrett writes about the FBI and the Justice Department for The Washington Post and is the author of “October Surprise: How the FBI Tried to Save Itself and Crashed an Election.” He was part of a team that won a Pulitzer Prize in 2018 for national reporting, for coverage of Russian interference in the U.S. election.