The Guardian breaks with its past and endorses Clegg's party. The main reason: electoral reform:

Proportional representation – while not a panacea – would at last give this country what it has lacked for so long: a parliament that is a true mirror of this pluralist nation, not an increasingly unrepresentative two-party distortion of it. 

The Guardian has supported proportional representation for more than a century. In all that time there has never been a better opportunity than now to put this subject firmly among the nation's priorities. Only the Liberal Democrats grasp this fully, and only they can be trusted to keep up the pressure to deliver, though others in all parties, large and small, do and should support the cause. That has been true in past elections too, of course. But this time is different. The conjuncture in 2010 of a Labour party that has lost so much public confidence and a Conservative party that has not yet won it has enabled Mr Clegg to take his party close to the threshold of real influence for the first time in nearly 90 years.

This time – with the important caveat set out below – the more people who vote Liberal Democrat on 6 May, the greater the chance that this will be Britain's last general election under a first-past-the-post electoral system which is wholly unsuited to the political needs of a grown-up 21st-century democracy...

Surveying the wider agenda and the experience of the past decade, however, there is little doubt that in many areas of policy and tone, the Liberal Democrats have for some time most closely matched our own priorities and instincts. On political and constitutional change, they articulate and represent the change which is now so widely wanted. On civil liberty and criminal justice, they have remained true to liberal values and human rights in ways that the other parties, Labour more than the Tories in some respects, have not. They are less tied to reactionary and sectional class interests than either of the other parties.

The Liberal Democrats were green before the other parties and remain so. Their commitment to education is bred in the bone. So is their comfort with a European project which, for all its flaws, remains central to this country's destiny. They are willing to contemplate a British defence policy without Trident renewal. They were right about Iraq, the biggest foreign policy judgment call of the past half-century, when Labour and the Tories were both catastrophically and stupidly wrong. They have resisted the rush to the overmighty centralised state when others have not. At key moments, when tough issues of press freedom have been at stake, they have been the first to rally in support. Above all, they believe in and stand for full, not semi-skimmed, electoral reform. And they have had a revelatory campaign. Trapped in the arid, name-calling two-party politics of the House of Commons, Nick Clegg has seldom had the chance to shine. Released into the daylight of equal debate, he has given the other two parties the fright of their lives.

A newspaper that is proudly rooted in the liberal as well as the labour tradition – and whose advocacy of constitutional reform stretches back to the debates of 1831-32 – cannot ignore such a record. If not now, when? The answer is clear and proud. Now.

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