Which is why Ed Miliband's comments in the New Statesman today are so eyecatching. He tells Jason Cowley and Mehdi Hasan that he couldn't go into the coalition with the Lib Dems if they were led by Nick Clegg. He's got problems with "what [Clegg] is supporting," you understand.
This is a new approach from one of the Labour leadership candidates. Until now, they've all tended to treat Lib Dems as a single mass – and a mass that deserves a good shoeing. But, here, Miliband explicitly recognises the party's internal divides. The clear implication is that Nick Clegg is too Tory for his, or Labour's, tastes* – and that he could do business with someone who leans more to the left. Stand up Vince Cable, or Mr Hughes, perhaps?
I'm not sure whether this is smart or dumb politics from Miliband. Sure, it shows that he is willing to engage with the Lib Dems on some level, and could it sabotage Lib Dem internal relations. But he's also setting the bar for a LibLab coalition quite high – after all, deposing a party leader is never the smoothest, nor most predictable, of processes. Besides, on the back of an election defeat, perhaps Labour shouldn't be dictating the terms of negotiation quite yet.
* A message which could be reinforced by, erm, today's Spectator leader praising the Lib Dem leader.