From Richard Nixon to Ted Kennedy, not to mention a certain Muhammad Ali: US politics and sport are studded with comebacks that disprove F Scott Fitzgerald's thesis that there are no second acts in American lives. Third acts, however, are uncharted territory. But an answer will be provided by the next chapter in the epic NFL career of Brett Favre.
Tonight, when the reigning Super Bowl champion Steelers host the Tennessee Titans in Pittsburgh, marks the start of the new season for the sports league that vies with the Premier League as the world's richest and most hyped. But the season's most compelling storyline is surely the third coming of Favre, a quarterback legend with the Green Bay Packers, a bust with the New York Jets – and now the designated saviour aiming to lead the Minnesota Vikings to a first Super Bowl in franchise history.
The Vikings had been eyeing Favre ever since spring 2008, when he somewhat acrimoniously parted ways with the Green Bay Packers, the team where he had made himself an NFL legend. Instead he announced his retirement, before abruptly changing his mind and signing with the New York Jets a month before the start of the new season.
And by mid-November last year, more than half-way through the schedule, a fairy tale was on the cards as Favre led one of the league's doormat franchises to the top of their division. But then his throwing arm gave way and the Jets fizzled, failing to make the play-offs.
So Favre retired again and this time, it was assumed, for keeps. He already owned a raft of NFL passing records, his place in the Hall of Fame was certain. Why risk making a fool of himself? But like the gunslingers of the old West, to whom his thrilling, high-risk playing style is so often compared, he couldn't let go.
As late as 28 July, Vikings head coach Brad Childress had let it be known that his entreaties had failed, and Favre was out of the game for good. Three weeks later word got out that the Vikings had sent a private jet to bring Favre back from his farm in Mississippi, to the frozen north where he had earned gridiron immortality. The second "retirement" had lasted all of three weeks.
Next month, Favre turns 40, that is 10 years older than the average retirement age for players in a brutal sport. His trademark designer stubble is now a whiter shade of grey and his reactions inevitably are a fraction slower than in his heyday. "I'd be the first to admit, I don't think I am capable of making some of the plays I used to make," Favre has said. But "understanding my limitations, how it pertains to what we are trying to do, is now a part of this process. All I want to do is win. There is nothing like it."
This second melodramatic about-turn in the space of 12 months was of course perfect fodder for the late night shows: "My God," remarked David Letterman of CBS apropos of Favre's $25m (£15m) two-year deal with the Vikings, "talk about Cash for Clunkers" (a reference to the federal government's programme to get ancient gas-guzzlers off the road).
But enough of the old mystique remained for the Vikings to sell an extra 2,000 season tickets within hours of the news. And not surprisingly. The Letterman skewering was no more than a backhanded compliment to a man who is one of the great quarterbacks in history. This year, assuming he stays healthy, he could break the consecutive games record of 282 held by the former Vikings defensive end Jim Marshall.
Far more importantly, this grizzled veteran, with the No 4 as always on his jersey, could be the missing piece that enables the Vikings – already one of the best defensive teams in the NFL – to go deep into the play-offs, conceivably all the way to Super Bowl XLIV in Miami on 7 February next year. For that of course, Favre's arm will have to hold up.
Perhaps ominously, his 2008 showing with the Jets was one in a series of recent late-season declines, which had led the Packers to conclude their interests were better served by a younger option. His return, even Childress admits, is a calculated gamble.
The Vikings' opener, against the Cleveland Browns on Sunday, will be an early pointer to whether the bet pays off. But it is a mere curtain-raiser to what will surely prove the most piquant moment of the 2009 season, when Favre steps out on Lambeau Field in Green Bay, to play before the fans who once worshipped every blade of grass he walked on.
Calling the play: Quarterbacks with a point to prove
In the universe of the NFL, they are the sport's glittering supernovas, the best known, most pressurised (and usually best paid) players, the pivots around whom everything revolves. This season they are under scrutiny as rarely before – and not only Brett Favre.
In Philadelphia, Michael Vick, once the best remunerated player in the NFL, has a chance with the Eagles to remake a career almost destroyed by a dog fighting scandal. But can he do it? And can the team combine his undoubted talents with those of proprietary quarterback Donovan McNabb? Upon the answer depends the Eagles' chances of winning their first Super Bowl.
In Boston, the focus is on just one man, Tom Brady, back after missing almost all of 2008 through injury. Without him, the team barely made the play-offs. With him, the New England Patriots, who went all the way three times between 2002 and 2005, could do so again.
In Cincinnati, meanwhile, the potential man of the hour is Carson Palmer, also back from season-wrecking injury, aiming to prove the Bengals can spring some surprises in 2009.
The story is similar in Washington, where Redskins fans are praying Jason Campbell can lead an underperforming and sometimes dysfunctional franchise back to the glory days of 20 years ago. In Phoenix, all eyes are on Kurt Warner, now 38. Can he, like Favre, defy the years and carry the Arizona Cardinals one step further than last February, when they lost a thrilling Super Bowl to the Pittsburgh Steelers?