Eighteen months ahead of general election day, former Lib Dem defence minister Nick Harvey is confidently calling the result. "Labour has already won," he tells the Huffington Post's Ned Simons. Harvey rightly points to the mass defection of Lib Dem voters to Labour as the key point in Ed Miliband's favour. As I recently noted, Labour continues to retain the support of more than a quarter of 2010 Lib Dem voters, a swing greater than the cumulative increase in the Conservative vote between 1997 and 2010.
The exodus of voters from Clegg's party is the main reason why, despite suffering its second worst defeat since 1918 at the last election, Labour has now led in the polls for three years. Significantly, as Lord Ashcroft's recent study of 2010 Lib Dem supporters noted, they are less likely to return to the fold than other voters. Ashcroft observed that "those who have moved to Labour are the most likely to say they are sure how they will vote (78%). This compares to just over a two thirds of those who say they would vote Conservative (69%), just under two thirds of those who say they would vote UKIP (62%) and less than half of those who would vote Green (42%)."
If this patten is repeated at the general election, the Tories stand to lose dozens of seats - there are 37 Conservative-Labour marginals where the third place Lib Dem vote is more than twice the margin of victory. As Harvey says, "The collapse of the Lib Dem vote with most going to the Labour party means that the Tories have probably lost two dozen seats before they even get out of bed."
While existing Lib Dem MPs, many of whom enjoy large local followings, are likely to benefit from an incumbency effect, it is the Tories, not Labour, who will suffer as a result; Cameron's party is in second place in 38 of the Lib Dems' 57 seats.
The replacement of Clegg with a more left-wing figure, such as Vince Cable or Tim Farron, could have helped to shift the odds back in the Tories' favour, but the moment for that has passed. Right now, it is hard to see how the Lib Dem recovery that the Tories so badly need will happen.