Worthy talk, for sure. But as his disquisition on world voting structures clocks 10 minutes, it has grown as intricate and winding as a Californian gerrymander and shows no sign of letting up. Hertzberg, though, is so amicable, so obviously enjoying himself, it feels churlish to interrupt.

As The New Yorker's main writer of the weekly Comment essay, Hertzberg has a voice that stands out for its warmth and common sense. Novelist Philip Roth has praised its 'uncommon journalistic modesty', at odds with the shrill bellicosity typical of the commentariat.

He's a bleeding-heart liberal but also a master of takedowns, drawing blood from the cruel hard-right. After Hertzberg charged former House Speaker Newt Gingrich with homophobic bigotry, Fox News host Bill O'Reilly dispatched reporters to ambush Hertzberg on his way to work, then on his nightly news programme aired the full exchange with the bemused and pre-caffeinated writer.

Yet Hertzberg is more an observer than an arguer - the sequence of words in the subtitle to Politics is deliberate. Though he acknowledges writing predominately for those who already agree with him - as most of The New Yorker's million-plus readers surely do - he tries to avoid inflammatory language that could alienate others. To those within the left-liberal church, he's known for his unflappable charm and seems to have no enemies.

Above all, Hertzberg is a brilliant wordsmith. Although his analysis is usually unimpeachable, it's his prose that most distinguishes him. In Hertzberg's thinking, journalism is no art but a means to an end: 'It's like a trade. It might be in the category of interior design or clothes design - maybe architecture, at best. Philosophy, religion, literature, music and science are ends in themselves; those are the really important things.'

Not that Hertzberg aspired to anything but journalism. In his early 20s, he lined up as a pacifist and radical, joining the Young People's Socialist League and contributing to the War Resisters League magazine, Win. He has since moved towards the centre, but says that's more 'a matter of style and maturing than really an important shift'.

The emerging newshound's main training ground was the Harvard Crimson, the student daily at Harvard University, where he was managing editor. William Shawn, then the editor of The New Yorker, had a son in Hertzberg's year, and noticed his work in the Crimson. When Shawn called and said in his soft voice, 'Hello, this is William Shawn', Hertzberg replied, 'Yes, and this is Marie of Romania', before hanging up. Only when Shawn phoned again did Hertzberg believe the caller was actually the legendary editor inviting Hertzberg to join his staff, rather than a student prankster.

Hertzberg didn't take up the offer - not immediately - feeling too green for The New Yorker. The possibility of being drafted to Vietnam also concerned him; so he opted for a one-year draft-deferred post as editorial director of the US National Student Association (NSA), where he edited a magazine aimed at inculcating students throughout the world with American values.

Not until the following year, while working for Newsweek, did he learn the NSA was funded by the CIA. 'The selling point abroad had always been that our Soviet counterparts were obviously KGB operations,' recalls Hertzberg, 'so it was a crushing blow to discover that we and the Soviets were two peas of a pod.'

In 1966, he enlisted in the navy. Upon being ordered to Vietnam two years later, he wrote a 25,000-word application for conscientious objector status. His file was rejected, but he was mustered out due to a mild medical complication, ending his fantasies of heading to jail as an anti-war hero. So Hertzberg phoned 'Mr Shawn', as he was generally known, and took an office at The New Yorker.

The Shawn-era New Yorker was an outsized cash cow, which bankrolled a large and mostly unproductive staff. 'You really had to motivate yourself,' says Hertzberg, recalling the three-day weekends and long holidays. But the freedom made him feel isolated and angst-ridden about his writing abilities, and he started seeing a shrink.

For a change of pace, he worked as a speechwriter for New York governor Hugh Carey. Within months, he was tapped by a Harvard alumnus to be a speechwriter for president-elect Carter, later becoming chief speechwriter. 'There was a real exhilaration to the feeling of taking sides and being in the political arena, rather than just peeking over and looking at the fight,' says Hertzberg.

Another old school-tie opportunity arose when Martin Peretz, formerly his politics tutor and by then the owner of the New Republic, invited Hertzberg to edit his magazine. Peretz remains to this day a committed foreign policy hawk, but he wanted a more dovish editor to preserve the magazine's liberal tradition.

The two were at constant loggerheads - over affirmative action, the nuclear freeze movement, the Nicaraguan Contras. Peretz fired Hertzberg in 1984, only to reinstall him in the editor's seat five years later. 'It took another three or four years for me and Marty to sufficiently get on each other's nerves to part ways again.'

Meanwhile, at The New Yorker, advertising revenues were falling, and there was an increasing feeling that the magazine, which had hardly changed since it was founded in 1925, sorely needed to reinvent itself. So, in 1992, British journalist Tina Brown, famous for her circulation-boosting editorships of Tatler and Vanity Fair magazines, became the new editor.

When current editor David Remnick replaced Brown in 1998, he scaled back some of her PR buzz and sharpened the magazine's political focus, appointing Hertzberg to his perch as chief pundit.

In October 2008, they collaborated on a full-throated 4,000-word endorsement of Barack Obama. The editorial was a suitable olive branch for the Obama campaign, after The New Yorker ran a much-maligned cover depicting Barack and Michelle Obama as Islamic fundamentalists. Hertzberg wasn't involved in the decision to publish that cover, but he concedes the parody misfired: 'It should have had a little Fox News logo to make its satiric purpose clear.'

The New Yorker explicitly endorsed a presidential candidate, Democrat John Kerry, for the first time in 2004, after Hertzberg and Remnick decided they needed to do everything possible to prevent the re-election of George W. Bush.

When Obama persuaded BP to establish a US$20 billion escrow account to compensate the victims of the Gulf of Mexico oil spill, Republican Joe Barton described the fund as a 'shakedown'. Hertzberg responded in The New Yorker that 'unlike his most vociferous Republican critics, [Obama] is trying to move the country away from its abject subservience to oil. A shakedown? What Obama is trying for, in his methodical, sometimes maddening way, is a shakeup.'

The magazine's tone has changed unmistakably since the departure of Bush, as Obamamania has replaced Bush-baiting. 'I've never been more enthusiastic about a candidate for president than I was for Obama,' he says. 'I can't believe I've lived to see somebody of that quality elected president.

'When it comes to writing about the meaning of America,' Hertzberg goes on, 'no one except Lincoln has done better than Obama. He gets the vast, vast complexity of it - the strange mixtures and interflows of identity. It was because of Dreams from My Father [part two of Obama's autobiography] that I really became an Obama devotee.'