The Tories' problem is not Iain Duncan Smith but their political strategy

The critical question that the Conservative Party has to resolve is not whether to get rid of Iain Duncan Smith. It is whether there is an alternative leader who would be better.

The fact that Mr Duncan Smith has only been leader for 13 months is irrelevant. That is long enough to judge the character of a national politician. Of course, Mr Duncan Smith may yet have hidden depths or, more likely, an extensive and mildly interesting hinterland, but we already have the measure of the man. In politics, as in the rest of life, first impressions are lasting impressions.

And the Tory leader has some positive qualities. He has a better sense of strategy than William Hague, understanding the centrality of the public services, and he has a straightness of character that contrasts with Tony Blair's actorly slipperiness.

But his weaknesses are serious. He has no hold over an audience, and not much of one over his party. He has offended both modernisers and traditionalists, and has signally failed to enlist the party's heavy-hitters of yesteryear to his cause.

It may seem surprising so soon after a reasonably successful party conference that Tory MPs are plotting to get rid of him. But they are not being too melodramatic or too impatient, nor are they leaping prematurely to judgement, in observing that his chances of leading them to victory at the next election are, in one of Michael Portillo's favourite words, nugatory.

It is telling that, in his interview in The Independent, his defence against the whisperers is to point out that Margaret Thatcher was written off as Leader of the Opposition in 1975-79 (although her personal rating was low, the party was ahead of Labour in the opinion polls before 1979). That is no basis for his "guarantee" that he will lead the party into the next election.

Mr Duncan Smith does not offer positive reasons why he should survive, perhaps because he knows that all the obvious challengers are hobbled in some way; Kenneth Clarke by his Europeanism, David Davis by his unpredictability, Theresa May by her feebleness, Michael Portillo by his poor judgement.

If there is an alternative leader, he or she must therefore emerge from the ranks of those who are still below the radar. But that will not save Mr Duncan Smith if Tory MPs decide that there is a political opportunity that he is failing to grasp. In this case, the leadership question turns back from personalities to issues.

The question for the Conservatives becomes whether or not the economic slowdown opens up a weakness in New Labour that they can exploit. The theme is clear enough: smaller state, lower taxes. Before the plotters go any further, they have to decide whether there could be a market for such a proposition if it were sold with the kind of confidence, conviction and brio that Mr Duncan Smith seems unable to muster. They have to decide whether the Conservative leader has been hypnotised by Mr Blair into trying to fight for the same centre ground, or whether the conventional wisdom in favour of higher taxes and higher public spending is phoney.

It will certainly be interesting to see what effect the one percentage point rise in national insurance contributions has on public opinion next April. And it would be refreshing to see the Tories try to start a real political argument about taxing and spending. But for the moment, a leadership challenge is more likely to make the Conservatives' predicament worse rather than better.