The Saturday Essay: Bill Clinton used to be known, with good reason, as the Comeback Kid. Clearly, for all his supernatural powers, the former President was never a match for the Prince of Darkness.

Bill Clinton used to be known, with good reason, as the Comeback Kid. Clearly, for all his supernatural powers, the former President was never a match for the Prince of Darkness, the unsinkable (or do I mean unkillable?) Peter Mandelson. A third return to front-line politics is not actually without precedent, but to return after having twice resigned in disgrace is less a comeback than a resurrection.

That Mr Mandelson also appears to have made peace with Gordon Brown is beyond remarkable. They chose their sides in the Borgia court of new Labour fully 14 years ago, and the poison has flowed freely ever since. Either Mr Brown is now confident of his position, and ready to make use of every talent available, or he is desperate.

Mr Mandelson is not without qualifications: minister without portfolio, Trade Secretary, Northern Ireland Secretary, European Trade Commissioner. He is not without a ton of well-known baggage, either, from mortgage loans to passport applications to his adjutant's role in the Blair-Brown wars. It is all a long way from the Young Communist League, perhaps, but most things are. As Business Secretary, Mr Mandelson should play a pivotal role in Mr Brown's embattled cabinet. If, that is, old habits have died, soft or hard.

Clearly, Downing Street has taken his latest appointment very seriously. These days, a reshuffle "surprise" means only one thing: no-one leaked a word. That has become rare. The fact that even Mr Mandelson has proved a model of restraint and discretion is also a novelty.

One of the obvious ideas at work behind his appointment seems to have been to trump David Cameron's conference speech. That would explain the timing: here's more priceless experience for your novice to chew on. But all that is, or should be, the least of it.

Mr Mandelson certainly has experience, and parts of the cabinet are light in that regard. From his European job, the new minister will bring a contacts book few domestic politicians can match. If he does not understand a great deal about global trade and finance by now, he never will. Any senior minister can make the calls; this one, as often as not, will be talking to people he already knows.

If all goes well - and who would bet on that? - yesterday's man reborn grants Mr Brown another asset. Mr Mandelson, once code-named "Bobby" by the Blairites, is regarded as someone who knows how to win elections. The Prime Minister has a looming problem in that respect, the biggest, if you trust the polls, any governing British politician has ever faced. If Mr Mandelson can turn things round he will be worth a peerage and a third chance.

But will Lord Mandelson be the Lord of Misrule? Will he behave himself, personally and politically? Or will he be unable to resist when Mr Brown's furtive rivals whisper their loyalty to the Blair legacy? You might have thought there would be other things for a Business Secretary to worry about, just at the moment, but Mr Mandelson, reformed character or not, is the prisoner of his reputation. Where he goes, speculation follows.

Try one tantalising question. What does Alistair Darling, the Chancellor, think of all this? It was surely tricky enough to deal with one countervailing force in the economic field in the shape of a Prime Minister who ran the Treasury for a decade. If Mr Mandelson is bringing expertise and a great deal of experience to the game, relationships could become crowded. He may intend only to do his bit for the country in a crisis. Mr Darling might wonder.

The Prime Minister, at any rate, believes, or wants to believe, or wants us to believe, that disruption will be kept to a minimum. Perhaps gratitude overwhelms Mr Mandelson. Perhaps Mr Brown meant what he said when he told us he would do whatever it takes to get Britain out of a mess. The appointment of the new Business Secretary is clearly intended as a masterstroke. But if ever the phrase "failed politician" adhered to an individual, it sticks to Mr Mandelson.

We could, perhaps should, judge the exercise by its results. We could also wonder what all those internal Labour wars were ever really for, and whether the appointment does not prove that the government is perilously short of fresh talent. Some voters will certainly wonder about the political system that allows Mr Mandelson his rehabilitation, and wonder what he has done to deserve it.

True, he has said in the past that he "always believed" Mr Brown should succeed Tony Blair. There would have been mayhem had he said otherwise. Labour, as the party these days forgets, could find no-one willing or able to oppose Mr Brown, or even to appear to match him in stature. Now, belatedly, Mr Mandelson, too, has seen the light. Apparently.

An economic crisis should keep him busy enough. He would not be Peter Mandelson, however, if he did not allow his thoughts to turn now and then to the task of returning Labour to office. No-one ever plays one game at a time in Westminster. As things stand, Mr Brown's only chance of winning a General Election hinges on, first, taming an economic crisis; secondly, consequently, on taming David Cameron. Lord Mandelson will be consulted.

Even after its recent dip, Mr Cameron's poll lead would put the Tories into power. Even after reclaiming some ground, Mr Brown remains spectacularly unpopular, as the Glenrothes by-election will prove. So what did Mr Cameron reveal in his much-admired conference speech? I heard every word, and I summarise: he has "character" aplenty, but very few policies he cares to share with the British electorate.

This amounts to a remarkable proposition now a commonplace in western opposition politics. Policies, actual ideas, are rationed like credit. They say this is to prevent the theft of good notions by governments, or to prevent today's bright thoughts being overtaken by events. All very rational, yet all very strange: vote for me, but I can't tell you why.

Mr Cameron remains very popular in England, in any case, so what do I know? Mr Brown, meanwhile, remains a figure of loathing, this week because he has failed to guarantee all bank deposits absolutely. And the country is in deep trouble. If Mr Mandelson is to enter this fray - he will - the peer-in-waiting must relish a challenge.

Still, this is, after all, Peter Mandelson under discussion. Look beyond the scandals and all judgments are personal. Mine is that his reappearance at the heart of the Labour Party is depressing, somehow, whatever I think of Labour. When half the world is shouting for "change", real or imagined, the dark prince returns to government. I was tempted at one point to call him the Third Man, but I have seen that movie too often, and I know how it ends. Not well.

Still, never forget the wisdom of Lyndon Baines Johnson. Old LBJ once said he judged it better to have his enemies inside the tent, relieving themselves on the outside world, than outside pissing in. Now there was a man who knew his way around a crisis.