His premiership was blighted by Iraq. But what if he'd said 'No' to George W. Peter Preston ponders what might have been.
Supposing grew fashionable 15 years ago when the author Robert Harris of Fatherland fame supposed where Britain would be if Hitler had won the war.
Supposing is almost an epidemic today, as a departing Blair faces various supposed trials for supposed Baghdad mendacities. But let's - because supposing is a game anyone can play - suppose something different. Suppose Blair's Britain, like Chirac's France, had steered well clear of Iraq.
It is March 2003 and the US has 100,000-plus crack troops poised in the zone. Australians, Poles and numerous small fry are there or thereabouts. But France and Russia and now Britain are staying out. The weapons inspectors need more time, they say. Resolution 1441 doesn't sanction invasion. (Lord Goldsmith is quite clear on that.) So what happens next?
What was always going to happen - the Americans blast in anyway. Saddam folds. That toppling statue stars on TV screens around the world. "Mission accomplished!" cries George Bush. Freedom lives! Moreover, at a subsequent press conference, he voices his sorrow over "what must be the end of our special relationship. Since Winston Churchill, Great Britain has been our staunchest friend. We gave it our bomb, our help in the Falklands. We came to its rescue in 1944. But now, in our own war after 9/11, that friend has turned its back. All Americans will be especially saddened and shocked."
Not just all Americans - Democrats as well as Republicans, lining up to vent Senate spleen - either. Here are Duncan Smith's Tories, lashing Labour's reluctance to follow their lead. Here are rather a lot of Lib Dems, opposing (because that's what oppositions do). Here are "sources close" to Gordon Brown, wondering openly whether "Tony hasn't lost his b***s", and "intelligence experts" leaking indignation that their "unanimous view" about weapons of mass destruction (WMDs) has been pushed aside.
President Chirac congratulates London on "following my lead". Israel (and numerous columnists) denounce "Blair's moral funk". Media barons Rupert Murdoch and Conrad Black turn the fire of their assorted organs against "shameful appeasement". "Can Blair survive?" asks the Independent as Brown heads (again) to Cape Cod for the holidays.
Things turn a bit more sour for the US through the summer, of course. Iraqis don't line the streets cheering any longer. What, no WMDs? We were always doubtful, say intelligence experts. But, back in Britain, the attack is relentless. Where are our contracts to rebuild Iraq, asks the Confederation of British Industry? Where are our tourists, ask tourist boards? Why should Edinburgh hotels pay for London's folly, asks Alex Salmond? A scheduled Blair visit to Washington goes west. The Queen's 2007 trip is "in jeopardy", according to the Sunday Express. And visa waivers are on the way out, just like any hope of a Kyoto accord.
Surely, though, life gets a tad easier here as Iraq goes into meltdown. Curiously not. No friends in the White House means warmer welcomes elsewhere. Cue Daily Mail fury: "Blair crawls for safety to Brussels." Cue the Sun on "the new lapdog of Europe". BBC Newsnight's Jeremy Paxman curls a practised lip: "Why are you so lily-livered, prime minister?" asks the inquisitor. And the Times makes an essential point that will last four more years: "Blair's folly has deprived America of the wise counsel it needs at this time of stress."
Damned if you do and damned if you don't, eh? Lord Goldsmith must go, says the Express. Alastair Campbell goes jogging. Perhaps Gleneagles 2005 will be recovery moment? But 7/7 in Russell Square puts paid to that.
"Now perhaps Britain will listen," says vice-president Cheney (in loco Bush, who has stayed in Crawford nursing a cold).
Washington ships 25,000 Pakistanis back to Heathrow. Rupert Murdoch reckons that "Blair should be in Guantánamo himself" at a party, but "he was probably only joking", a spokesman claims.
Somehow in desperation and despair, the main man hangs on. Somehow, the chancellor is afraid to strike.
Somehow American casualties stretching into the thousands take the pressure off a Blair-Brown scrap. But "this was the war Blair could have stopped", cries the Mirror. "We traded safety for influence, and lost," concludes the Financial Times. "Moi! Je suis le special relation maintenant," claims Sarkozy.
And, nearly 10 years to the day since he started, the local elections turf him out. "His 27 per cent legacy," says The Guardian. "Faithless voters desert faithless Blair," says the Mail. But "I'm off," cries the PM, flying the coop. "It's time to do something else." Not a surprise ending, I suppose.
Peter Preston was editor of The Guardian from 1975 to 1995 and now writes columns for the paper (this was published last Monday) and for the Observer.