For most of this parliament there were strong reasons for assuming a slaughter of the Liberal Democrats at the forthcoming election. The party has lacked a defining issue such as the war in Iraq. David Cameron is perceived in some quarters to have moved on to their terrain. The media had paid most attention to the battle between Gordon Brown and Cameron, sensing the Liberal Democrats were increasingly irrelevant.
Suddenly the solid reasons seem very shaky. A series of disparate events, all of them vaguely connected, combine to give Nick Clegg an opportunity that seemed unimaginable even six months ago.
The most important change comes in the form of the mighty opinion polls, those trackers of fickle opinion that determine the political mood. Several polls point to a hung parliament. For now it does not matter whether such polls prove to be right on election night. Their significance is in their impact on the current situation. They give the Liberal Democrats an apparent importance that a thousand speeches from their leader or the revered Vince Cable cannot deliver. From seeming marginal, Clegg becomes a potential player, a leader with troops who could make a difference.
The narrowing of the Conservatives' lead reflects the second element of the changed situation. As I argued on Tuesday, Cameron's policies are finally coming under a degree of scrutiny: the rootless, focus group driven oscillations in relation to their plans for "tax and spend"; the unreformed Euroscepticism; and the wider contradictory objectives. Suddenly the unquestioned common assumption that Cameron has moved his party on to the centre ground is being questioned a little. Or at least there is recognition that this untested, inexperienced political leader moves his party to the centre and then back to the right on a regular basis. As a result of such insecure manoeuvring, space opens up for the third party.
Labour is more overtly accommodating. The most optimistic of ministers hopes for nothing more than a hung parliament at the election. For different reasons they would celebrate such an outcome as much as Clegg. The possibility is the main reason why Brown has pledged a referendum on the Alternative Vote after the election.
Cameron had good cause to mock Brown's conversion during Prime Minister's Question Time yesterday, quoting from Paddy Ashdown's diaries in which Brown is accurately portrayed as the main block to electoral reform during the 1990s (although Blair was another significant obstacle. He never believed in it and accidentally told me so in an on the record interview in the summer of 1995).
Brown was outrageously disingenuous when he answered questions in front of the Liaison committee of MPs on Tuesday when he claimed with an innocent air that it had been impossible for the government to get consensus on the question of electoral reform after 1997. He was one of the reasons why there was no consensus.
I am told that Clegg is as scathing privately about Labour's belated conversion to a new voting system as he is publicly. Who can blame him in the light of the pre-election timing and Labour's self-interested unreliability since 1997? Nonetheless the conversion has significance. In the 1997 election Blair pledged a referendum on the voting system but did not indicate where he stood on the issue. Brown and the entire Cabinet will enter this election advocating change.
In some cases ministers act out of expedient desperation, in others their support reflects a genuine desire to bring about realignment on the centre left. None of them would be quite so keen if Labour was 20 points ahead in the polls. But Labour is not anywhere near being ahead and had been behind for nearly all of this parliament, a context in which Clegg receives overtures whether he seeks them or not. Being the recipient of overtures is flattering for the leader of a party that is always in danger of being ignored at a national level. Overtures imply significance and the media takes note.
The fact that Brown is well behind in the polls persuaded him to back televised debates with the party leaders, another potential gift to the Liberal Democrats. Clegg will be the first Liberal Democrat leader in the party's short history to reach a huge television audience. I bumped into David Owen the other day who told me how such an opportunity would have been a dream for him when he was leader of the SDP in the 1987 election and an extremely authoritative media performer.
Clegg is understandably wary of the feverish anticipation, aware that if expectations of his performance are high the post-debate verdict might be less than flattering. Like the other leaders he is also acutely conscious that the whole event could be an anti-climax, with the need for precise balance and a tightly agreed format being constraints to lively exchanges. Still the TV extravaganzas are a big chance for him and not surprisingly he is starting to prepare for them already, another sign that the three debates are going to dominate the election campaign.
Brown has given one other gift to Clegg in the form of the Iraq Inquiry. Indeed Brown's pre-election appearance is the consequence of a question from the Liberal Democrats' leader. Almost certainly most voters are not following the Inquiry with the same intensity as parts of the media, which report developments that are seven years old as if they are breaking news. Even so senior Labour figures are rightly worried that the Inquiry is a daily reminder of the greatest foreign policy calamity since Suez and one that vividly brings to life the wider flaws of the New Labour project and its crusading timidity.
The Tories were more gung ho than Labour and have in their shadow cabinet some of the more devout believers in the neo-conservative cause, the heirs to Blair in more ways than one. As the opponents of the war the Liberal Democrats stand to gain a little one more time as the arguments are revisited in the run-up to the election, perversely with a greater media intensity than in the 2005 campaign, even though the conflict was much more recent then.
These recent developments give Clegg some room to breathe, which is the best a Liberal Democrat leader can hope for. They shape a context which is more propitious in some ways than the one in which Paddy Ashdown operated when Blair could have swallowed the Lib Dems alive, and almost as good as the one Charles Kennedy enjoyed after he had been vindicated over the war.
Can Clegg make the most of it? His room for movement is limited after an election even in the event of a hung parliament. There is little point asking him what he would do in such circumstances because he would not be fully in control of his party. The leader of the Liberal Democrats is constrained by what is known as a "triple lock" in relation to a coalition.
Clegg would need the agreement of his MPs, the party's executive and the membership. By the time he had secured such agreement a Prime Minister, let alone the rolling television news channels, would have collapsed with impatience. There is no guarantee he would get such agreement anyway. It is not going to happen. There will be no coalition.
But in the build-up to the election Clegg's pro-European, anti-Westminster, redistributive liberalism gives him an authentic and distinctive voice. At least he knows his voice will be heard when not so long ago it seemed as if he'd be drowned out by the clamour of the two bigger parties. We will have to wait and see whether he will take it, but he has a chance.