In the modern era political parties are both pathetically fragile and surprisingly robust. They are doomed to fragility with dwindling memberships and the eternal scrutiny of rolling news. Yet most of the time they remain intact. As Tony Blair took Labour to the right there were no high-profile defections. Under Gordon Brown's leadership Blair's more ardent followers displayed signs of fuming misery, but remained in the fold and are still not tempted to join the Conservatives or the Lib Dems. Only once since 1945 were the boundaries of party politics dramatically reshaped, and that was when senior Labour figures formed the SDP. Most of the time parties keep their vaguely defined shape.
This is one of the reasons why there is a powerful case for arguing that the Liberal Democrats will emerge from the trauma of the student fees affair in reasonable shape. While we in the media enjoy speculating about epoch-changing splits, they rarely happen.
More specifically, Nick Clegg has a clearly worked out strategy in which, at least up until the referendum on electoral reform, he seeks to show that two parties can work together in a sprit of unity. As the next election moves into view he will emphasise more explicitly his party's distinct contribution.
One of Clegg's allies also points out to me that quite a few of the party's potentially trouble-making MPs hope to be ministers. Never underestimate the power of patronage in keeping a governing force together. And of course there is the powerful instinct for a party to unite for fear that any alternative route will lead to oblivion. As the senior Clegg ally put it to me, "Aftertuition fees we hug the Conservatives more closely, not less."
These are all reasons for assuming that the Liberal Democrats will sail through the stormy seas. Yet the very strength of parties also presents a potentially fatal problem for leaders who move away from a significant section within them. Blair did push at the boundaries of his party over Iraq and in his agreement with David Cameron over public-service reforms. The consequences were not fatal, but Labour's identity crisis, currently taking the form of absurdly premature attacks on Ed Miliband's leadership, arises from the boundary-challenging Blair era.
The Liberal Democrats' reputation so far has suffered largely over the issue of trust, a deadly theme as Blair discovered, but one that is not policy-based. There are some at the top of their party who believe that now the tuition fees' vote has taken place, the worst is over. There are no equivalent landmines to come.
This is not the case. The cuts in local government, where Liberal Democrats have a strong base, are more devastating than those imposed on universities. At least universities have an alternative source of funding in the form of the tripling of fees, even if the rise is recklessly steep. But councils are planning big cuts in services. My local authority has sent out a questionnaire asking residents to give a view on which cuts they would prefer, or loathe less: "Some libraries closed or all of them staying open for fewer days a week?" The questionnaire puts the debate about cuts and the Coalition's extreme response to the deficit in a more tangible light.
Then there are housing benefit cuts already opposed by some senior Liberal Democrats, an overhaul of the NHS and a reform of policing accompanied by cuts in police numbers. The Liberal Democrats have joined forces with a group of Tory radicals that are moving Britain rightwards at the speed of a high-speed train (which the Coalition rightly wants to launch). The wing of the Liberal Democrats that does not regard public spending as a sin and virtually all government activity as illiberal will be more than tested.
Already it responds to the test. On Sunday the party's deputy leader, Simon Hughes, gave a revealing interview to The World This Weekend in which he pleaded for progressives to stay in the party, adding "We need progressives more than ever", presumably to counter perceived non-progressives at the top of his party.
Until now Hughes has been utterly loyal in interviews. This time his tone was very different, conveying resolute despair. Separately, the party's former director of policy Richard Grayson has argued that most Lib Dem members have more in common with their counterparts in the Labour Party and the Greens than with their own leadership. As a journalist who has attended every Lib Dem conference since its formation, that is the impression I have formed too. Compare Grayson and, to some extent, Hughes with Clegg's echo of Blair on Iraq. The Lib Dem leader has noted several times: "It's worse than you think. I believe in these policies."
While these immediate challenges engulf a party there have been important changes of direction in the other two that makes a distinct identity for the Liberal Democrats more elusive. At the top of the Conservatives the leadership is now socially liberal. Under Miliband's leadership Labour will be more balanced in its approach to civil liberties after a period of nervy authoritarian populism. Miliband was also opposed to the war in Iraq.
This leaves the Lib Dems without a unique cause over which they can easily unite. Instead, the defining issue of our times is the economy, the role of government in bringing about a stable recovery and in the provision of public services. On this the Lib Dem leadership sides with the Conservatives, while others in the party are closer to Labour.
At some point before the election, the largely suppressed alarm will have no choice but to erupt, as it did within Labour's ranks in the early 1980s. This could take the form of defections, a more permanent realignment with the Conservatives among Cleggite Liberal Democrats, or even a challenge to Clegg's leadership.
Given the strength of tribal loyalties I am surprised at the conclusion I reach, but I cannot see how a party carries on like this for another four years. Something will happen, especially if the party's poll ratings sink even lower. How ironic that a groundbreaking coalition leads to a familiar battle over the economy and public services between one set of views on the centre left and another on the right.
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