But this creates problems for Brown so far as tonight's TV debate and the rest of the election are concerned. His instinct may well be to repeat the "I agree with Nick" positioning of last week. But this has already been heavily lampooned - and was batted away quite comprehensively by Clegg the last time he tried it. And, what's more, if Labour aren't seen to properly combat the Lib Dem tide, then they risk, erm, consolidating their third-place position in the polls - which could, in turn, decrease the likelihood of a LibLab coalition.
If Brown gets the balance wrong tonight, then you can expect that the underwhelming, underperforming nature of Labour's campaign will become a bigger story than it is now. And rightly so.