After yesterday's volley of attacks on the Lib Dems, Labour has continued the theme with its new party election broadcast, which depicts Nick Clegg as the "un-credible shrinking man". In the black and white film, the Lib Dem leader is shown diminishing in size as his Tory superiors overrule him and triple tuition fees, raise VAT introduce the bedroom tax and cut taxes for millionaires.
Opinion on the broadcast's artistic merits is divided (it's not the best PEB I've seen, but far from the worst), but what about the politics? My former NS colleague Mehdi Hasan asks why Labour is bothering to attack a party that currently sits in fifth place in the European election polls. But a year away from the general election, the film is a signal that Labour recognises the importance of retaining the support of the electorally crucial group of Lib Dem defectors.
With around 25 per cent of 2010 Lib Dems currently supporting the opposition, it can't risk going soft on Clegg and handing them "permission" to return (as some already have). In addition to those seats that Labour can hope to win directly from the Lib Dems, strategists point out that in 86 of the party's 87 Tory targets, the Lib Dem vote share in 2010 was larger than the Conservative majority. In 37, it is more than twice as large. Even if Clegg's party partially recovers before 2015, Labour stands to make sweeping gains.
The Lib Dems' decision not to replace Clegg with a more left-wing figure such as Vince Cable or Tim Farron has limited the potential for the party to make a fresh appeal to the electorate. But with both coalition parties increasingly obsessed with differentation, Labour clearly recognises the potential for the Lib Dems to recover ground as May 2015 approaches. With two polls today putting them just a point ahead, they can't afford to allow Clegg the opportunity to do so.
A third of 2010 Lib Dems are undecided, with one in five considering UKIP. Which side they come down on will be crucial to determining whether Labour wins.
In his conference speech last year, Clegg memorably listed 16 "heartless" Conservative policies he had blocked. Labour's mission is to remind voters of those he has enabled (one party source ridiculed his claim to be "equidistant"). When you study the numbers, it's not hard to work out why.