How Bill Clinton brightens a room. Last week he dropped into town to celebrate Nelson Mandela’s 90th birthday. One minute he was hobnobbing with Elton John and Robert De Niro at a charity dinner – corporate tables a snip at £100,000 – the next he was seen leaving No 10 in what the fashion writer of The Times gushingly described as “a dazzling pistachio shirt, an eye-popping striped tie and a raffish summer jacket in dove grey, the season’s most fashionable shade”.

The only raincloud on our man of mode’s sunny horizon was Mandela’s pronouncement that Zimbabwe was suffering because of “a tragic failure of leadership”. I hope such talk didn’t bring back unhappy memories, as Clinton is quite the expert on African genocide and failures of leadership.

Back in 1994, when he was president, the Hutu government of Rwanda murdered 800,000 Tutsi and moderate Hutu within the space of 100 days. The weapons were primitive – machetes, spades and garden tools – but the results were highly efficient, the fastest killing spree in history. Clinton later apologised for failing to “appreciate the gravity” of the situation.

Actually Bill’s administration did appreciate it. Washington had helped remove UN peacekeepers from Rwanda, blocked the sending of UN reinforcements when 8,000 a day were being murdered, and refused even to jam radio broadcasts used by the government to coordinate the killings.

A year later Clinton was at it again, or rather not at it again, during the mass murder of thousands of Bosnian Muslims in Srebrenica in 1995. This time he refused even to change the flight path of an American spy satellite to find out what was going on: it would have been too embarrassing.

Clinton is, of course, loved by good liberals everywhere, while his successor George Bush and Tony Blair are reviled for the invasion of Iraq; they were or are deluded pawns of sinister neoconservatives and starry-eyed neo-liberals who want to prop up democracies on the back of western bayonets.

Now I don’t want to be too hard on dear Bill. He eventually came round to tipping the balance against evil in Bos-nia. And when the Serbian leader Slo-bodan Milosevic threatened the ethnic cleansing of the Albanian population of Kosovo his friend Tony Blair persuaded him, after a series of screaming matches on the phone, to commit American ground troops.

Today humanitarian intervention has, in any case, been widely discredited after the disaster that followed the toppling of the genocidal dictator Saddam Hussein, hasn’t it? The antiAmerican left and the little England right unite in scorn for the Texan cowboy and his British poodle.

But what’s that I hear? Massacres of Muslims by Muslims have approached genocidal proportions in Darfur, Sudan. “Something must be done,” cry the do-gooders of the left. In Burma, the generals let their people die in the wake of devastating floods rather than accept contaminating western aid. “Send in the US air force,” bellow the critics of American bombers.

The little Englanders have changed their tune, too. Fire-eaters are now calling for Britain and America to oust Mugabe, even though they have condemned all other allied interventions.

There is only one thing worse than humanitarian intervention by the West, it seems, and that’s no intervention.

The calls for action grow stronger as Zimbabwe’s pulse grows fainter. Our government has failed to persuade the South Africans to turn Mugabe out, as they can at any time, though as Peter Hain hinted in these pages last week, we haven’t tried very hard.

Forty years ago Britain didn’t act to remove the illegal white minority government of Ian Smith in Rhodesia when it was propped up by apartheid South Africa. Today Britain doesn’t want to topple Smith’s nemesis, Mugabe, against the wishes of the white regime’s enemy and successor, the ANC government of Thabo Mbeki. We gave Mugabe a knighthood after he massacred his enemies in Matabele-land. But he was “a good chap” then. Conservative and Labour policy alike on Zimbabwe has been crippled by postcolonial guilt or inverted racism.

In any case, an overstretched, second-rank power like Britain would find it difficult to force its will on a landlocked opponent without the cooperation of the neighbourhood – though Zimbabwe’s army is no obstacle.

Mugabe jeers: “How can the ball-point fight with the gun?” Alas, he is right. Perhaps the disapproval of Man-dela and, more important, that of Mugabe’s African neighbours heralds an end to his illegitimate rule. I have my doubts. For the moment we can tighten the sanctions screw. But if the horrors threaten to mount to Rwandan proportions, shouldn’t we act?

Back in 1999, at the height of the Kosovo crisis, Tony Blair gave a celebrated speech in Chicago drafted by my old war studies tutor, Professor Lawrence Freedman, setting out principles for humanitarian intervention. Somehow it evaded the Foreign Office censors. It deserves reading in full, but here are his key tests for action.

“First, are we sure of our case? War is an imperfect instrument for righting humanitarian distress; but armed force is sometimes the only means of dealing with dictators. Second, have we exhausted all diplomatic options? We should always give peace every chance. Third, on the basis of a practical assessment of the situation, are there military operations we can sensibly and prudently undertake? Fourth, are we prepared for the long term? In the past we talked too much of exit strategies. But having made a commitment, we cannot simply walk away once the fight is over; better to stay with moderate numbers of troops than return for repeat performances with large numbers. And finally, do we have national interests involved?”

The Chicago speech was not a charter for American gunslingers to go riding out in an outlaw world. Blair knew that idealism had to be tempered by realism. He understood that democracies are rightly reluctant to sacrifice the lives of their servicemen. He set limits to western ambitions: no, we are not going to get rid of dictatorships where the balance of risk is all wrong.

Blair’s critics have a point, too, that the first and second tests were not applied in Iraq, though even Saddam’s allies thought he had chemical weapons. In Afghanistan and Iraq, President Bush and his defence secretary, Don-ald Rumsfeld, failed the fourth test by pig-headedly refusing to plan for the postinvasion settlement. In our magazine today you can read how the remarkable US general David Petraeus, exponent of “the surge”, is trying to make up for that deficit in Iraq, though even he acknowledges that military victory will be insufficient without “moral legitimacy”.

Blair concluded his speech like this: “I say to you: never fall again for the doctrine of isolationism. The world cannot afford it. Stay a country outward-looking, with the vision and imagination that is in your nature. And realise that in Britain you have a friend and an ally that will stand with you, work with you, fashion with you the design of a future built on peace and prosperity for all, which is the only dream that makes humanity worth preserving.”

Windy talk of “dreams” and “humanity” usually gives me indigestion, but I believe, in essence, Blair was right. British engagement with an outward-looking America is always better than the alternative. I see no reason in theory why an Anglo-American planB could not be devised to topple Mugabe’s tinpot government if thousands more are starved and axed to death. Most of the Chicago tests are easily passed in Zimbabwe’s case. The second, that of exhausting all diplomatic means, alas, could soon be met. Only the last, that of cold national interest, is debatable – although we should be able to look our children in the eye when they ask us what we did.

When he was chancellor Gordon Brown won a reputation for his concern for debt-laden African countries. Now the prime minister and his idealistic Foreign Secretary, David Miliband, may have to face a hard choice. To watch as more die or to push for intervention. I’m sure they won’t want to go down with Bill Clinton as leaders who couldn’t “appreciate the gravity” of an African tragedy.

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