Nick Clegg has sprinkled adose of salt into the prime minister's European wounds this morning. The deputy prime minister has written an article in the Observer  insisting that the coalition will be "measured" in its approach to any proposed changes to Brussels institutions and warns that "retreating to the margins" of Europe would be "economic suicide".
David Cameron, meanwhile, has told the BBC's Andrew Marr that he would like to see further "rebalancing" of powers with regard to Brussels, but recognises that the Conservatives must act as a coalition - an unveiled hint that it is only the Lib Dems that stop him from giving full rein to his own more Eurosceptic impulses. It is obvious why he would want to present that argument - persuading Tory back benchers that his hands are tied with yellow Lib Dem cord. I'm not sure it will do him much good. The Conservative hard core anti-EU faction know perfectly well that the Lib Dems are an impediment to their ambitions and see Cameron's deference tothem as weakness. Hearing the prime minister advertise that problem will hardly placate them.
Part of Cameron's problem here is that he is trapped in an inherently dishonest position. He probably would like the UK one day to have a different relationship with Brussels, but recognises it is impractical - politically and diplomatically - to demand one now. He would almost certainly have come to the same conclusion if he had a majority in parliament. There are, in government, simply better things to be getting on with, especially in an economic crisis. So Cameron will not march into the European Council swinging a Thatcheresque man-bag demanding more control of employment rights legislation or anything else - and not because the LibDems won't allow it, but because it is not a priority for him. The back benchers know it, so there is very little the PM can say that will satisfy them.
One factor that could really change the dynamic is the performance of Ukip - or rather, Nigel Farage's party's anticipated performance in 2014 European elections. Ukip has already beaten the Lib Dems in a couple of by-elections and is a natural repository for disgruntled Tory protest votes. One poll out today  puts Ukip within easy striking distance of the Lib Dems nationally. Conservative strategists are, apparently, very worried about what that might mean for a poll that is due just a year before the next general election. It is feasible to imagine that, come 2014, Cameron will be more afraid of Farage's populist, nationalist agitation beyond the gates of his coalition than Clegg's cosmopolitan Europhile hand-wringing within.