In febrile economic and political times, leadership comes under even more intense scrutiny than usual. Occasionally there is speculation about whether David Cameron and Ed Miliband will still be leaders of their parties by the next election. The focus on Nick Clegg is greater and more persistent.

On one level, there are good grounds for the introspection within the Liberal Democrats. Their poll ratings are abysmal and threaten to decimate them as a parliamentary party. Mr Clegg's personal ratings are dire. More specifically, Mr Clegg has failed to implement the two constitutional changes with which he was directly associated: electoral reform and a more democratic second chamber. As Deputy Prime Minister he is formally linked to a Conservative Party that still pursues a radical policy agenda rooted firmly on the right.

Undoubtedly there are many policies that Mr Clegg can point to in mitigation and, equally important, to Tory-instigated proposals that he has vetoed. But he cannot deny the evidence of the polls or that he is trapped in a perhaps unavoidable, but nonetheless deeply dangerous, political contortion.

Not surprisingly, there are a few public voices hinting at the need for a change of leadership. Indeed, the surprise is that there have not been more such voices over the past two years. The former Treasury spokesman in the Lords, Lord Oakeshott, has been characteristically vocal. His words carry more weight now that his friend, the Business Secretary Vince Cable, indicated a willingness to lead earlier in the summer. No wonder Mr Clegg returned from his holidays hailing vaguely the need for a wealth tax, a sign of insecurity as his party conference looms.

Dissenting Liberal Democrats need to make their moves extremely carefully. They have shown they can be ruthless, removing Charles Kennedy and Sir Menzies Campbell during the last parliament. But this is the first time since their formation that they have to reflect on leadership in power.

The reflections have an impact on the country as well as their party. In terms of the country, there is little to be gained by insurrectionary noises now. The economic situation is already frighteningly unpredictable without mid-term fever over Mr Clegg's leadership. Of much greater practical use is for nervy Liberal Democrats to put as much pressure as possible on Mr Clegg to ensure that the second half of this Parliament is more focused on economic growth.

Mr Clegg and his close ministerial allies must become much more assertive in the Coalition. Mr Cameron cannot do without them at the moment, so they have more power than they sometimes appear to realise. Mere words and posturing are not enough. But what is certain to cause inept impotence is never-ending feuding over who should be the party's leader now. Such a scenario is neither in the interests of the party nor the country.

That does not mean the leadership question is irrelevant. It might become urgent and legitimate as the next election moves into view, again both in terms of the interests of the Liberal Democrats and the country. In his somewhat confused interview earlier this week, Mr Clegg seemed to accept that his party has lost permanently the support of some left-of-centre voters while making a headline by proposing a wealth tax, a policy that is more readily seen as one espoused by those on the left of centre.

Vince Cable would not be so dismissive of left-of-centre voters and might be able to win back some of them. He also enjoys a reasonable relationship with Ed Miliband, a partnership that might assume importance after the next election. But that is for another day. For now, senior Liberal Democrats must focus on what they can do with their limited power and, as Paddy Ashdown argued yesterday, give full support to their leader.