Tony Blair's enemies know many different things. They know that dissent is the life-force of democracy. They know that a lively politics needs different kinds of people in it; rough and uncomfortable people as well as smooth and well behaved people.

They know that New Labour is underplaying the plight of the very poor, including the employees of British sweatshops, and losing its attraction to core supporters as a result. They know that the policy gap between Labour and the Conservatives is too close to be credible. And those are important things to know.

But Tony Blair knows one bigger thing. He knows that John Major can win the next general election.

Consumer spending is growing. Mortgages are, in terms of recent history, very cheap indeed. House prices in the South are moving again. Inflation remains low. Insecurity remains rife and there may be little room for tax cuts. But in most respects, these are good times for people in employment. None of which has helped the Tories much so far (although the poll gap is slightly narrowing). But with the aid of a huge anti-Labour advertising campaign now underway, and the luck of a run of anti-Blair stories in the press,Major can still turn the tide.

That singular possibility is Blair's big fact. For most of political Britain - the politicians, the civil servants, the media, the lobbying groups - the possibility of a fifth Conservative victory has become unmentionable, virtually undiscussed, seemingly unthinkable. Who outside Central Office seriously debates the Tory agenda for the early 2000s, or gossips about who Major might want as his chosen successor after another successful campaign? What a herd we are.

But whatever Blair is, he isn't a herd animal. He has quite enough imagination to see how another Tory government could happen. He rates Major as a fighter. He knows the potential wealth and awesome power of the Tory machine. And he also knows that part of the story it needs to tell involves the return of the old Labour left and a revival of trade union militancy.

In these circumstances the job of a leader is to keep his eye on the big fact, ruthlessly excluding secondary facts, however interesting or emotive they might be.

Blair's instinct is supported by the public's hostility to split parties. In the end, the election may come down to an argument about which of the main parties is the most badly split, and hence the least effectively led. So far, the Tory split seems infinitely more serious than the Labour one. Blair, unsurprisingly, wants to keep it that way.

So, whatever one thinks of his particular decisions - on Clare Short, Scottish Home Rule, whatever - it is hard to deny Blair's central logic, or to fault his tenacious concentration on the essence of the game.

Nor does he want to be remembered as a conservative. In an article for the Independent on Sunday last weekend, Blair himself made the point that the politics of opposition were very different from the politics of government. His message was: not radicalism now, but radicalism soon ... trust me.

That is not, on the face of it, an unreasonable tactic. In a land where tabloid hysteria rages so wildly, it may be the only plausible one for a moderate reforming party to adopt. But it is, or will be, difficult. The trouble is that, at some point, Labour's leadership has to remember all the smaller things that its internal critics are worried about - the need for pluralism, some dissent, more outspokenness, the "condition of Britain" question. The trick is to win power by ruthless concentration on the game of winning power; and then to be able to play a different sort of game.

This switch has been achieved before. Roosevelt did it in the Thirties, turning from fiscal conservative to champion of "the forgotten man at the bottom of the economic pyramid". Coming from another direction, one could argue that Margaret Thatcher did it in the Eighties, turning from conventional Tory to, well, Thatcherite. But it is a difficult trick. It means unlearning in office much of what you learned in opposition. It means rediscovering the qualities of people who had been irritating, and eagerly reaching for issues from which you had once shied away. It means courting danger and media unpopularity when necessary.

But unless this transformation occurs, it will be difficult for a future Labour government to alter the climate of politics. And the party must achieve that revival of hope if it is to be successful not merely during one week in the spring of 1997, but for many months and years afterwards.

Today, our politics are conducted in a sticky, conservative, energy-draining climate, in which the big issues (Europe, poverty, the environment) are not argued between the parties, and hence at the ballot box, but inside the parties; where frankness is shunned; where Westminster politics seems ever less part of the life of the rest of the nation. It is not a climate in which any reforming government can thrive.

Without, in short, an injection of unpredictability, straight talking, real argument and courageous radicalism, our precious democracy is in danger of boring itself to death. Those are the dissenters' small things which Blair can ignore while he concentrates on winning. But if he wins, his understanding of them will determine his success or failure in power.