Something happened when the political tribes were on holiday, and now, as the conference season comes round again, they have still not caught up with the new balance of power. The important event occurred on or about 3 August, when David Cameron told the Deputy Prime Minister that it would not be possible to get House of Lords reform through Parliament, and that he had decided to abandon the Bill.

Nick Clegg responded as he had warned the PM that he would. He withdrew Liberal Democrat support for the changes to constituency boundaries that would have given the Conservatives an advantage. It was politics as gangland tit-for-tat killing. Like the divorcing Kavanaghs, the lawyers who by last week had spent most of their £3m assets on suing each other to their last £90,000, the Prime Minister and his deputy said to each other: "You can't have Lords reform." And, "In that case, you can't have your new boundaries."

Formally, the boundary review, to cut the number of constituencies and make them more equal in size, continues. The final report is due in October next year. But even if Clegg could persuade some of his 57 MPs to vote for new boundaries, which change his Sheffield seat into a Labour winnable, there are also about 25 Tories who would lose out. Cameron has accepted defeat. One of the first things that Grant Shapps, the new Tory chairman, did when he was reshuffled this month was to tell local parties to choose candidates for the next election on existing boundaries.

Thus the coalition is in terrible shape. "Part of our contract has now been broken," as Clegg put it when Lords reform was ditched. The air is thick with recrimination Ω although I am told that Cameron and Clegg are polite and businesslike with each other Ω and yet, with their boundaries bonus gone, the Conservatives will need the Lib Dems more than ever in 2015.

According to Peter Kellner of YouGov, the Tories need to be seven points ahead of Labour in share of the vote to gain a bare majority in the Commons. Conversely, Labour, although only four points ahead in our ComRes poll today, needs to be just one point ahead for a majority. The Tories were seven points ahead in the 2010 election, but that was not enough for a majority because the Lib Dems won so many seats. Next time a majority looks even further away, because nearly half of the Lib Dems' 2010 support has gone over to Labour.

So Cameron still needs the Lib Dems. But he does not necessarily need Clegg. He, like the rest of us, must have watched incredulously as the Deputy Prime Minister decided that the way to deal with tuition fees, his most serious mistake, was to make a YouTube video about it before his party conference. He must have watched again, with redoubled incredulity, as the video, remixed to music, became a hit, magically softening the bitter edge of voter rage. But he knows that Clegg is still a liability not just for the Lib Dems but for the coalition, and no amount of computer-generated singing can turn him into an asset.

That is why the Vince Cable phenomenon is the story of this week's Lib Dem conference. Recent opinion polls, including today's from ComRes, suggest the party would do better if Clegg were replaced by the Business Secretary. Such findings are unusual: alternative leaders are rarely well-known enough. Yet, just now, two party leaders are stalked by more popular shadows: Vince and Boris. The only recent precedent was Gordon Brown: polls briefly suggested that Labour would do better with him as leader before the 2005 election.

Such polls are not always an accurate guide to what would happen if the leadership were to change. When Brown eventually took over from Tony Blair, the polls had long ceased to suggest a boost to Labour support. Yet Labour's ratings shot up and stayed high before crashing to new lows when Brown bottled out of a snap election. But they offer party members and MPs hope, and Lib Dems, facing disaster at the election, are likely to invest their hopes in avuncular Vince.

Some of us are entitled to be Cablesceptics. He was ministerially responsible for the trebling of tuition fees, and yet a side-effect of the Cleggapology remix is that it further distances Cable from that decision. That is how politics works. Labour was, for example, more enthusiastic than the Tories about Britain's membership of the European Exchange Rate Mechanism. Yet Labour benefited from the Conservative government's humiliation by the failure of the policy 20 years ago last Sunday.

Others point out how little Cable has achieved on industrial policy at the Business Department, a department he wanted to abolish in opposition and about which he may have been right first time.

None of that matters. He is someone of whom people have heard who has the huge asset of not being Clegg. However illogical, a change of leadership would let the Lib Dems parcel up the unpopular baggage of being in coalition and throw it overboard. It would in the interests of Lib Dem MPs (apart from the member for Sheffield Hallam). And, as the ditching of the boundary changes showed, brute political interest is a powerful force.

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