Rudolph W. Giuliani had always been hard to miss at the Grand Havana Room, a magnet for well-wishers and hangers-on at the Midtown cigar club that still treated him like the king of New York.In recent years, many close to him feared, he was becoming even harder to miss.For more than a decade, friends conceded grimly, Mr. Giuliani’s drinking had been a problem. And as he surged back to prominence during the presidency of Donald J. Trump, it was getting more difficult to hide it.On some nights when Mr. Giuliani was overserved, an associate discreetly signaled the rest of the club, tipping back his empty hand in a drinking motion, out of the former mayor’s line of sight, in case others preferred to keep their distance. Some allies, watching Mr. Giuliani down Scotch before leaving for Fox News interviews, would slip away to find a television, clenching through his rickety defenses of Mr. Trump.Even at less rollicking venues — a book party, a Sept. 11 anniversary dinner, an intimate gathering at Mr. Giuliani’s own apartment — his consistent, conspicuous intoxication often startled his company.“It’s no secret, nor do I do him any favors if I don’t mention that problem, because he has it,” said Andrew Stein, a former New York City Council president who has known Mr. Giuliani for decades. “It’s actually one of the saddest things I can think about in politics.”No one close to Mr. Giuliani, 79, has suggested that drinking could excuse or explain away his present legal and personal disrepair. He arrived for a mug shot in Georgia in August not over rowdy nightlife behavior or reckless cable interviews but for allegedly abusing the laws he defended aggressively as a federal prosecutor, subverting the democracy of a nation that once lionized him.Yet to almost anyone in proximity, friends say, Mr. Giuliani’s drinking has been the pulsing drumbeat punctuating his descent — not the cause of his reputational collapse but the ubiquitous evidence, well before Election Day in 2020, that something was not right with the former president’s most incautious lieutenant.Now, prosecutors in the federal election case against Mr. Trump have shown an interest in the drinking habits of Mr. Giuliani — and whether the former president ignored what his aides described as the plain inebriation of the former mayor referred to in court documents as “Co-Conspirator 1.”Their entwined legal peril has turned a matter long whispered about by former City Hall aides, White House advisers and political socialites into an investigative subplot in an unprecedented case.The office of the special counsel, Jack Smith, has questioned witnesses about Mr. Giuliani’s alcohol consumption as he was advising Mr. Trump, including on election night, according to a person familiar with the matter. Mr. Smith’s investigators have also asked about Mr. Trump’s level of awareness of his lawyer’s drinking as they worked to overturn the election and prevent Joseph R. Biden Jr. from being certified as the 2020 winner at almost any cost. (A spokesman for the special counsel declined to comment.)Mr. Giuliani was one of the most public faces of Mr. Trump’s effort to overturn the 2020 election. Erin Schaff/The New York TimesThe answers to those prompts could complicate any efforts by Mr. Trump’s team to lean on a so-called advice-of-counsel defense, a strategy that could portray him as a client merely taking professional cues from his lawyers. If such guidance came from someone whom Mr. Trump knew to be compromised by alcohol, especially when many others told Mr. Trump definitively that he had lost, his argument could weaken.In interviews and in testimony to Congress, several people at the White House on election night — the evening when Mr. Giuliani urged Mr. Trump to declare victory despite the results — have said that the former mayor appeared to be drunk, slurring and carrying an odor of alcohol.“The mayor was definitely intoxicated,” Jason Miller, a top Trump adviser and a veteran of Mr. Giuliani’s 2008 presidential campaign, told the congressional committee investigating the Jan. 6 attack on the Capitol in a deposition early last year. “But I do not know his level of intoxication when he spoke with the president.” (Mr. Giuliani furiously denied this account and condemned Mr. Miller, who had spoken glowingly of him in public, in vicious terms.)Privately, Mr. Trump, who has long described himself as a teetotaler, has spoken derisively about Mr. Giuliani’s drinking, according to a person familiar with his remarks. But Mr. Trump’s monologues to associates can betray a layered view of the former mayor, one that many Republicans share: He credits Mr. Giuliani with turning around New York City after the high-crime 1970s and 1980s and contends that it has suffered lately without him in charge. Then he returns to a lament about Mr. Giuliani’s image today.Mr. Trump does not dwell on his own role in that trajectory.In a statement that did not address specific accounts about Mr. Giuliani’s drinking or its potential relevance to prosecutors, Ted Goodman, a political adviser to the former mayor, praised Mr. Giuliani’s career and suggested he was being maligned because “he has the courage to defend an innocent man” in Mr. Trump.“I’m with the mayor on a regular basis for the past year, and the idea that he is an alcoholic is a flat-out lie,” Mr. Goodman said, adding that it had “become fashionable in certain circles to smear the mayor in an effort to stay in the good graces of New York’s so-called ‘high society’ and the Washington, D.C., cocktail circuit.”“The Rudy Giuliani you all see today,” Mr. Goodman continued, “is the same man who took down the mafia, cleaned up the streets of New York and comforted the nation following 9/11.”A spokesman for Mr. Trump did not respond to a request for comment.Many who know Mr. Giuliani best are careful to discuss his life, and especially his drinking, with considerable nuance. Most elements of today’s Mr. Giuliani were always there, they say, if less visible.Long before alcohol became a concern, Mr. Giuliani was prone to sweeping, unsubstantiated claims of election fraud. (“They stole that election from me,” he once said of his 1989 mayoral loss, alluding to supposed chicanery “in the Black parts of Brooklyn and in Washington Heights.”)Long before alcohol became a concern, he could be quick to lash out at enemies real or perceived. (“A small man in search of a balcony,” Jimmy Breslin once said of him.)In interviews with friends, associates and former aides, the consensus was that, more than wholly transforming Mr. Giuliani, his drinking had accelerated a change in his existing alchemy, amplifying qualities that had long burbled within him: conspiracism, gullibility, a weakness for grandeur.A lover of opera — with a suitably operatic sense of his own story — Mr. Giuliani has long invited supporters, as Mr. Trump has, to process his personal trials as their own, tugging the masses along through tumult, tragedy, public divorce.Yet there is a smallness to his world now, a narrowing to reflect his circumstances.In August, Mr. Giuliani was booked at the Fulton County jail in Atlanta after he was charged in a sprawling racketeering case against Mr. Trump and his allies. Brynn Anderson/Associated PressHe faces a racketeering charge (among others) in Georgia, a defamation case brought by two election workers and accusations of sexual misconduct from a former employee (he has said this was a consensual relationship) and a former White House aide (he has denied this account).One of his lawyers has said Mr. Giuliani is “close to broke.” Another, Robert Costello, once a protégé of the former mayor’s, is suing him for unpaid legal fees.Mr. Giuliani’s circle has shrunk as old friends have fallen away. His law license was suspended in New York. The Grand Havana Room closed in 2020.Most days, Mr. Giuliani hosts a radio show in Manhattan, stopping for sidewalk selfies with the occasional stranger.Most nights, he stays in for a livestream from the apartment he long shared with his third ex-wife, Judith Giuliani. It recently went up for sale.“Rudy loves opera,” said William J. Bratton, his first police commissioner, to whom Mr. Giuliani once gave a CD collection of “La Bohème” as a gift. “Few operas end in a happy place.”A crushing defeat and a growing concernMr. Giuliani recording his weekly radio show from his office at City Hall in May 2000.Ruby Washington/The New York TimesMr. Giuliani was always the kind of elected official who kept opposition researchers busy: romantic entanglements, personnel conflicts, a trail of incendiary remarks.But as he prepared for life after City Hall — mounting a short-lived Senate campaign in 2000 and harboring visions of the presidency — Democratic operatives say Mr. Giuliani’s drinking was one issue that never came up.There was a reason for that. As mayor, former aides said, Mr. Giuliani did not generally drink to excess and expected his team to follow his lead.Part of this seemed to flow from insecurity: Reared outside Manhattan in a family of modest means, Mr. Giuliani always took care to keep his wits about him, one senior city official said, because he did not want to lower his guard in view of New York’s elites.Another consideration was practical. Mr. Giuliani thrilled to the all-hours nature of the mayoralty, hustling toward scenes of emergency to project authority and control long before 9/11 showcased this instinct to the wider world, and he was vigilant about staying ready.No one doubts that the attack, and his ascendant profile, profoundly reshaped him. On Sept. 10, 2001, he was the polarizing lame duck who had antagonized artists, warred gratuitously with ferret owners and defended his police department through high-profile killings of unarmed Black men — including one episode in which Mr. Giuliani attacked the deceased and authorized the release of his arrest record.By midweek, he had become a global emblem of tenacious resolve, held up as the city’s essential man. (Mr. Giuliani quickly came to see himself this way, too: With the election to succeed him weeks away, he began pushing by late September to postpone the next mayor’s start date and remain in office for a few more months, even asking the Republican governor, George Pataki, to extend his term, according to Mr. Pataki. The idea had few takers and was abandoned.)Mr. Giuliani’s political standing rose after the terrorist attacks on Sept. 11, 2001. Last year, he faced criticism for calling that day “in some ways, you know, the greatest day of my life.”Robert F. Bukaty/Associated PressThe years that followed were a swirl of mourning and celebrity — wrenching remembrances, lucrative business ventures, an honorary British knighthood — a tension that Mr. Giuliani can still sound as if he is struggling to reconcile.He faced criticism last year for calling Sept. 11 “in some ways, you know, the greatest day of my life.” He has also seemed haunted by it, no matter what doors it opened: After a colonoscopy in 2018, he told people then, he was informed that he had been talking in his sleep as if he was establishing a command center at ground zero when the towers fell.Mr. Giuliani’s stewardship in crisis was supposed to hypercharge his long-planned presidential campaign, enshrining him as the early Republican front-runner in 2008. It did not.Instead, the earliest accounts of Mr. Giuliani’s excessive drinking date to this period of campaign failure. Though any political flop can sting, those who know Mr. Giuliani say that this one, his first loss in nearly two decades, was especially shattering.When his big electoral bet on Florida ended in humiliation, Mr. Giuliani fell into what Judith Giuliani later called a clinical depression. He stayed for weeks afterward at Mar-a-Lago, Mr. Trump’s club in Florida. The two were not especially close friends but had known each other for years through New York politics and real estate.During his presidential run in 2008, Mr. Giuliani bet heavily on a strong performance in Florida, but finished third and dropped out a day later. Chip Litherland for The New York TimesAround this time, Mr. Giuliani was drinking heavily, according to comments Ms. Giuliani made to Andrew Kirtzman, the author of “Giuliani: The Rise and Tragic Fall of America’s Mayor,” published last year.“Literally falling-down drunk,” Mr. Kirtzman said in an interview, noting that several incidents over the years, in Ms. Giuliani’s telling, required medical attention. Mr. Kirtzman said that he came to consider Mr. Giuliani’s drinking “part of the overall erosion of his self-discipline.” (Mr. Giuliani has said he spent a month “relaxing” at Mar-a-Lago. Ms. Giuliani declined through her lawyer to be interviewed.)Some who encountered Mr. Giuliani after the campaign were struck by how transparently he missed the attention he once commanded, how desperate he seemed to recapture what he had lost.George Arzt, a longtime aide to former Mayor Edward I. Koch, with whom Mr. Giuliani often clashed, recalled watching Mr. Giuliani wander on a loop through a restaurant in the Hamptons, as if waiting to be stopped by anyone, while the rest of his party dined in a back room.“He would walk back and forth like he wanted everyone to see him, more than once,” Mr. Arzt said. “He just wanted to be recognized.”People close to Mr. Giuliani particularly worried about him as his third marriage began to fray, growing unnerved at snapshots of his behavior even at nominally sanctified gatherings, like an annual dinner for close associates around Sept. 11.Mr. Giuliani and his wife at the time, Judith Giuliani, standing at right, in 2005. She has said he fell into a depression and drank heavily after his 2008 election loss.Bill Cunningham/The New York TimesIn almost any company, Mr. Giuliani seemed liable to make a scene. In May 2016, he derailed a major client dinner at the law firm he had recently joined with a fire hose of Islamophobic remarks while drunk, according to a book last year by Geoffrey S. Berman, who would later become the United States attorney in Manhattan.At the 9/11 anniversary dinner that year, a former aide remembered, Mr. Giuliani appeared intoxicated as he delivered remarks that were blisteringly partisan — and tonally jarring for guests, given the event being commemorated.The next year, a longtime attendee recalled, the traditional dinner was scrapped. Weeks before the anniversary, Mr. Giuliani had been rushed to the hospital with a leg injury.After drinking too much, Ms. Giuliani would say later, the former mayor had taken a fall.Recklessness, grievance and increased isolationMr. Giuliani and Mr. Trump in September 2020. The former mayor still praises the former president, and has appealed to him for financial help. Al Drago for The New York TimesWith a few days left in the Trump presidency — and the specter of a second impeachment trial looming after the Capitol riot — Mr. Giuliani was unambiguous.Short on allies and angling for another public showcase, the former mayor did not just want to represent Mr. Trump before the Senate: “I need to be his lawyer,” Mr. Giuliani told a confidant, according to a person with direct knowledge of the exchange.By then, much of Mr. Trump’s orbit was quite certain that this was a bad idea. Mr. Giuliani’s legal efforts since the election had roundly failed. He was the source of infighting, highlighted by an associate’s email to campaign officials asking that Mr. Giuliani be paid $20,000 a day for his work. (Mr. Giuliani has said he was unaware of the request.) He was also destined to be a potential witness.Mr. Giuliani’s foray into Ukrainian politics had already helped get Mr. Trump impeached the first time. And for years, some in the White House had viewed Mr. Giuliani’s indiscipline and unpredictability — his web of foreign business affairs, his mysterious travel companions and, often enough, his drinking — as a significant liability.Before some of Mr. Giuliani’s television appearances, allies of the president were known to share messages about the former mayor’s nightly condition as he imbibed at the Trump International Hotel in Washington, where Mr. Giuliani was such a regular that a custom plaque was placed at his table: “Rudolph W. Giuliani Private Office.” (“You could tell,” one Trump adviser said of the nights when Mr. Giuliani went on the air after drinking.)Mr. Giuliani has said he does not think he ever gave an interview while drunk. “I like Scotch,” he told NBC New York in 2021, adding: “I’m not an alcoholic. I’m a functioning — I probably function more effectively than 90 percent of the population.”At the Grand Havana in New York, some steered clear when Mr. Giuliani’s near-shouting conversations gave him away.“People would walk by after he started drinking a lot and act like he wasn’t there,” said the Rev. Al Sharpton, a longtime antagonist and a fellow member at the cigar club. (Mr. Sharpton said he did indulge in a running gag: He and others who opposed Mr. Trump sometimes playfully encouraged a server to double Mr. Giuliani’s liquor orders before he went on Fox.)But Mr. Sharpton attributed the former mayor’s troubles to a different vice, as many friends have privately.“When he started running after Trump, I said, ‘This guy’s addicted to cameras,’” Mr. Sharpton recalled, adding that Mr. Giuliani “had to know the negative sides of Donald Trump.” Before long, Mr. Sharpton observed, Mr. Giuliani was “running with guys that he would have put in jail when he was U.S. attorney.”Mr. Giuliani can seem wistful now about the days when he held such influence — and fanatical about settling old scores and destroying new adversaries, forever insisting that he is denied his due.Reflecting on the death last month of his second police commissioner, Howard Safir, Mr. Giuliani swerved suddenly during his livestream into Trump-style projection, using the occasion to smear Mr. Safir’s predecessor, Mr. Bratton, with whom Mr. Giuliani fell out.“Maybe Bratton going to Elaine’s every night and getting drunk actually helped,” Mr. Giuliani said. (“If the show wasn’t so sad, it would be hilarious,” Mr. Bratton said via text.)Other complaints from Mr. Giuliani have been more current. Fox News stopped inviting him on, he has groused repeatedly, even though he was working to highlight scandals surrounding Hunter Biden — and was vilified for it — well before they became a prime Republican talking point.A television clip of Mr. Giuliani was shown during a hearing last year by the House committee investigating the Capitol riot and the events surrounding it. Doug Mills/The New York TimesMr. Giuliani’s home was searched, and his devices were seized, by federal authorities in 2021 as part of an investigation that produced embarrassing headlines and, ultimately, no charges, further inflaming his sense of persecution.He can seem wounded that some past friends have drifted away.“He feels betrayed by some of the friends who used to be his friends,” said John Catsimatidis, the billionaire political fixture who owns the local station that carries Mr. Giuliani’s radio show. “How’d you like to have those friends as friends?”While Mr. Giuliani does not seem to place Mr. Trump in this category — still publicly fawning over a man to whom he has appealed for financial help — their relationship has endured some strain. On Mr. Trump’s final weekend in office, he excoriated Mr. Giuliani in a private meeting, according to a person briefed on it.Last month, Mr. Trump’s club in Bedminster, N.J., was the site of a fund-raiser for Mr. Giuliani’s legal defense.But days later, on the Sept. 11 anniversary, Mr. Trump did not say a public word about the New Yorker most associated with the tragedy.Mr. Giuliani focused his objections elsewhere, remarking often on his allotted location among dignitaries at the memorial. “They don’t put those of us who had anything to do with Sept. 11 too close,” he said.Appraising his own legacy later that week on his livestream, where he called himself New York’s most successful mayor in history, Mr. Giuliani still seemed consumed by his standing now in his city.He also sounded resigned.“This crooked Democratic city,” he said, “would never have a plaque for me.”Olivia Bensimon More