To accuse a democratic politician of excessive calculation is a little like blaming an ice skater for too much balance. It is intrinsic to the profession. But the best politicians, like the best skaters, make you forget about the calculation and watch the show.

They cut through the necessary balancing act and make you see something a little deeper than technique: a sense of conviction, a glimpse of a firmer set of principles, an impression of a man or woman able to make judgments about a changing world from a robust set of definable views.

You don’t have to agree with those views all the time. In fact, the best politician can make you respect him or her while disagreeing vehemently.

I think that’s part of Gordon Brown’s surprisingly buoyant honeymoon. Yes, for all the denials, he seems to have followed the Philip Gould script. Yes, the blur of activity, even the occasional conservative surprise, has done its job in the polling. But voters also sense - from the contrast with Tony Blair and the lack of performance polish - that deep down, Brown is more than a set of tactics.

He went into politics for a reason. He is a recognisable, if reconstructed, leftist. He thinks government is more often the solution than the problem, that the successful deserve to have their wealth confiscated at higher rates, that he knows better than many people how to spend their money and live their lives.

In some ways it’s almost a relief to have someone in No 10 with those familiar kinds of Labour party beliefs. Unlike his predecessor, you really can pin him down. And his competence and sobriety deter middle-class panic. After a decade of centrist straddle and spin, some small balm of relief can be felt.

And this surely is David Cameron’s primary problem. He is Blair-like at the moment that Blairishness is suddenly unfashionable. When your opponent seems to be operating from a core of self-confident ideology, your own focus-grouped move to the soft centre seems almost dated.

There is a reason for the careful rebranding, of course. Cameron has emerged from a Tory wilderness. He learnt in that desert to be circumspect about the core Conservative values: low taxes, strong defence, personal responsibility, smaller government. And so the tactical adjustments - many necessary and vital - have obscured the firmer principles. This is not a problem Margaret Thatcher had.

But it is a problem that wilderness parties often confront. If Cameron had not shifted rhetorically and substantively towards the centre, he wouldn’t be a contender for the next election (and, despite the sudden Tory wobble, he still is). But if he cannot also show some core - and recognisably Tory - convictions, he will suffer the fate of an advertising slogan that has become outré.

He is, of course, afraid of this next move. Will it undo all the rebranding he has already achieved? Can he ever please the Tory right anyway? Will a feint back to the right only cement the impression of politics as PR?

The American parallel that most strikes me is one that may seem counter-intuitive. Cameron has a Hillary problem. Hillary Clinton learnt the hard way what it is to be a Democrat in a Republican era, just as Cameron has had to learn how to be a Tory in a new Labour era. Every time you open your mouth, you fear your opponents will corner you into the old liberal or Tory stereotype.

So you play relentlessly against type, and hedge yourself aggressively against critics, and aim for the golden centre ground where people will no longer even think of you as they once thought of your immediate predecessors.

Clinton is haunted by the spectre of Jimmy Carter, of liberalism, of the old left that became so stigmatised in the 1980s and was used to devastate the Clintons in the early 1990s. She still won’t call herself “liberal” in public.

Similarly, Cameron is haunted by Major and the “nasty party” and the Eurosceptic infighting and the stench of corruption of the last Tory government. He is haunted by the failures of post-Major Tory leaders to break free of this. And he is determined - rightly - to be different.

The problem with this strategy is that it makes you seem both afraid of your opponents (you suspect their ideology is more popular than yours) and more circumspect (you’re always trying to avoid a mistake that will reveal your true views). Voters can smell fear and they can smell pure positioning. Up against the humour-free grit of Brown, that’s fatal. In politics, “be not afraid” is good counsel.

Hillary faces not Brown but Barack Obama. And Obama is a post-Clinton Democrat in rather the same way that Brown’s era has emerged as surprisingly post-Blair. Clinton and Obama are of different Democratic generations. Clinton is from the traumatised generation; Obama isn’t. Clinton has internalised to her bones the 1990s sense that conservatism is ascendant, that what she really believes is unpopular, that the Republicans have the structural power of having a majority of Americans on their side.

Hence the fact that she reeks of fear, of calculation, of focus groups, of triangulation. She might once have had ideals keenly felt; she might once have actually relished fighting for them and arguing in their defence. But she has not been like that for a long time. She has political post-traumatic stress disorder.

Her classic formulation today - recently made to a group of Aids activists - is what it was before: “We’ll have as much spine as we possibly can, under the circumstances.”

Obama is different. He wasn’t mugged by the 1980s and 1990s as Clinton was. He doesn’t carry within him the liberal self-hatred and self-doubt that Clinton does. The traumatised Democrats fear the majority of Americans are bigoted, know-nothing, racist rubes from whom they need to conceal their true feelings and views.

The non-traumatised Democrats are able to say what they think, make their case to potential supporters and act, well, like Republicans acted in the 1980s and 1990s. The choice between Clinton and Obama is the choice between a defensive crouch and a confident engagement. It is the choice between someone who often hid her beliefs in a welter of fear; and someone who has faith that his world view can persuade a majority.

Clinton, like Cameron, is facing a wobble. Although she still leads Obama commandingly in national polls, he is outpacing her in fundraising, and new polls show him tying with her in New Hampshire and edging her in South Carolina. Clinton is furiously trying to calculate how much she needs to reassure her base with core beliefs and how much she still needs to hedge for the centre ground.

Cameron has exactly the same conundrum, but he has an advantage over Clinton. If he shifts in emphasis towards more classically conservative positions - on taxes, spending and the economy, for example - he has inoculated himself sufficiently as the antidote to the “nasty” party to avoid the old Tory trap. His environmental policy and his social inclusiveness - both welcome moves for modern Tories - can balance more conservative options on taxes, crime or terror.

Mercifully, he doesn’t provoke in people the same visceral response Clinton does either. His negatives are much lower. He has more space to move.

But the direction is nonetheless clear. He needs to recapture the Obama sense of conviction to add to his Clintonian gift for the centre. He needs to remind voters not just that he is a new kind of Tory - but that he is also a Tory.

Calculation is necessary - and the right-wing purists reveal a fatal indifference to gaining power. But conviction is also needed - a line he won’t cross, a patch of clear blue Tory sky between him and Brown.

And less fear, please. Much less fear. If you don’t confidently believe in your own core convictions, who else will?

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