Gordon Brown is not alone in regretting his failure to call an election in October 2007. When, as a new prime minister, he showed characteristic caution - despite double-digit leads in the opinion polls - and backed away from a snap election, it destroyed not just his long-term prospects but the short-term chances of Menzies Campbell's survival.
Elected leader of the Liberal Democrats in March 2006, Campbell hadn't enjoyed a Brown-style honeymoon, and questions about his leadership abilities persisted 18 months into the job. A general election in autumn 2007 would have given him the opportunity to re-establish his position at the top of the party.
However, it was not to be and with continuing rumblings about his age - what he calls the media's "fixation with trivia" - and agitation from within the party, Campbell, then 66, knew that his moment had passed. "Could I take the constant references to my age for another two years? Could the party?" he wrote in his 2008 autobiography. The questions were rhetorical.
If he feels bitter four years on, the signs are difficult to detect. In any case, the MP for North East Fife is probably too busy to worry. He sits on both the foreign and intelligence select committees and a year ago was sounded out by David Cameron for the role, eventually taken by Peter Gibson, as chair of the inquiry into alleged UK complicity in torture. In September last year, he joined the 2012 Olympic Games board. It's an appropriate appointment for a man who ran the 200 metres at the 1964 Tokyo Olympics and held the British record for the 100 metres (10.2 seconds) between 1967 and 1974.
For five days in May 2010, he had the ear of Nick Clegg - his successor as Lib Dem leader - who was weighing up an offer to join David Cameron's Conservative Party in government. It's a scenario he had been considering for some time. "When Gordon Brown nearly had an election, I was already thinking ahead to what the consequences might be if the result wasn't an outright victory," he tells me when we meet in his cramped but perfectly appointed parliamentary office, with its views of the Thames and Big Ben. Campbell, in a blue jacket and signature pink-and-sky-blue-striped tie, sits on the green bench that fills the window bay.
He says that, for reasons of "high principle and low politics", full coalition was Clegg's only option - high principle because a minority government would not have assured the markets that Britain was serious about addressing the financial crisis; low politics because the Lib Dems were not sufficiently "robust financially" to fight a likely second election.
Whatever the motivation, the price of coalition has been electoral collapse. Despite signs that the party's poll ratings are recovering from the lows of the spring (Campbell concedes that the uplift is "very gentle"), the Lib Dems were humiliated a month ago in an Edinburgh council by-election. The result mirrored defeats in the local and devolved assemblies elections in May, particularly in Scotland, where the Lib Dems' ratings - below 10 per cent in both constituency and list votes - were unexpected (their coalition partner did markedly better).
Before the election, Campbell had been bullish. He told one national newspaper that Scotland was different because of its "sensible voting system" (the additional member vote) and because "devolution creates a different political context". Such optimism proved unfounded.
May also brought heavy defeat in the referendum on electoral reform. Victory would have signalled progress towards a fully proportional system and would have lifted party spirits. In the event, not only was a move to the Alternative Vote defeated by a margin of two to one, but the campaign that preceded it was characterised by rancour. At the time, Campbell described some of the exchanges between coalition partners as "incendiary". Four months on, he is more sanguine. "I'm not sure that our hands were cleaner than theirs," he says. "Senior Conservatives expressed their views, sometimes in pretty rough terms, but Chris Huhne [the Energy and Climate Change Secretary] expressed his views in pretty rough terms [as well]."
It has had a positive effect, too, he says, in helping to clear the air a little between the two parties. "It was a way of sweeping up the rose petals from the Rose Garden," he says, referring to Cameron's and Clegg's first joint appearance as Prime Minister and Deputy PM on 12 May 2010, when their easy rapport surprised many.
In some respects, Campbell is the perfect coalition loyalist. Of Cameron, he says: "He looks as if he's a prime minister, he sounds as if he's a prime minister"; he believes that George Osborne is right to pursue his deficit-reduction plan ("I don't see an alternative that would give us a better chance of getting to the other end"); and he now supports the controversial Health and Social Care Bill ("The broad thrust of the bill, which is to give patients more influence and more choice, is something that is entirely consistent with Liberal democracy").
In other areas, he has been more rebellious. In late August, he was critical of Cameron's assault on the Human Rights Act after that month's riots, and last December he was one of 21 Lib Dems who voted against an increase in university tuition fees; he and Charles Kennedy were the most senior members of the party to do so. "I pledged myself to do that," he says. "I had my photograph taken on the steps of the student union at St Andrews University," where he is chancellor. Campbell has said that his credibility would have been "shot to pieces", had he done anything but vote No. By extension, does that mean those Lib Dems who signed the same pledge and then abstained or voted in favour of the rise - there were plenty of them, including Clegg - had their credibility shot to pieces? "They must decide for themselves," he says, and then speaks of how he had been pressured to reconsider his position: "I was subject to quite a lot of late-night telephone conversations with my friends in the party, now in parts of the establishment."
On the economy, too - despite broad support for the Osborne plan - he is increasingly at odds with many on the Tory benches. He believes that the 50p rate of marginal tax levied against those earning £150,000 or above should "stay for the foreseeable future". This is an odd position for Campbell, who put his leadership on the line by forcing his party to abandon the 50p tax. "Times change and policies have to change," he says simply. He also believes that the coalition should rethink the rise in VAT, introduced in January. He wants the government "to look at whether or not you could have a temporary reduction or something of that kind . . . I hope the Treasury will look at this seriously."
On the government's military action over Libyan skies, by contrast, Campbell is supportive. As Lib Dem foreign affairs spokesman in the early 2000s, he became the face of parliamentary opposition to the 2003 war in Iraq and was a regular guest on the nightly news programmes, coining the phrase "flawed prospectus" to describe Tony Blair's attempts to justify pre-emptive action against Saddam Hussein. He rejects the accusation that in Libya as in Iraq, the west is attempting to effect pre-emptive regime change. "It's tempting to concertina into that," he says, but points to UN backing and the "pressing urgency of the potential humanitarian disaster".
Campbell, an MP since 1987, is proud of his friendships across the aisle. He was close to the Labour leader John Smith, and Brown was an irregular commuting companion. He describes the former Conservative prime minister John Major as someone "I like very much". Tension with other parliamentarians is rare, though it does exist. He was said to have been highly critical of Danny Alexander's decision to advocate a windfall tax on North Sea oil and gas and of his sanctioning the closure of RAF Leuchars in Fife. Campbell wondered aloud about the "extraordinary coincidence" that RAF Lossiemouth in Moray, near Alexander's constituency, was spared in the defence review.
More damaged is his professional relationship with Huhne. The two were never close ("I'm an admirer of his competence" is as far as he will go) but, according to Campbell, Huhne was guilty of a breach of trust in January 2006 by breaking an assurance that he wouldn't put himself forward as a rival candidate to replace the departed Kennedy as leader.
“In a room very like this room, he shook me by the hand and said he would support me," Campbell recalls. "Half an hour later, he came back and said he was thinking again." In his autobiography, he notes: "We didn't shake hands when he departed for a second time."
When I remind him of those words, Campbell says: "Perhaps I have got a slightly old-fashioned view, but when you make commitments . . ." His voice trails off and he spends a few moments searching for the right formula. "I don't want to start a row where 'Campbell accuses Huhne of being disloyal', but if you can't have confidence within your party, it means being a leader is much more difficult."
That confidence was tested again in October 2007, during the final days of Campbell's leadership. Friends told journalists that Huhne was doing the most to agitate for his removal. "People on his behalf," he says now, incredulous that anyone would think he wouldn't find out. But a "nod and a wink" from a friendly journalist was all it took.
Naturally, if Gordon Brown had been bolder four years ago, the whole episode would have been avoided. Or, perhaps, simply delayed.
Jon Bernstein is deputy editor of the New Statesman