Cameron will be cursing the order of the debates. He’d much prefer to be attacking Nick Clegg on domestic issues than foreign affairs on Thursday. In terms of the structure of the debate, the advantage is with Clegg.
Cameron will be wary of exploiting some of the Clegg weaknesses on Europe for fear of looking like an old-school Tory. And Clegg has a few topics (Iraq and Afghanistan) where he can deliver a change message.
Running through the main debating points makes clear that this will be no walkover for Cameron.
1) Iraq — Upper hand to Clegg
Clegg plays the outsider with public opinion on his side. Neither Cameron or Brown have apologised for supporting the war. What response does Cameron have, apart from attacking Brown?
2) Afghanistan — Upper hand to Clegg
Public opinion is not yet in favour of an immediate withdrawal, but it is running in that direction. Clegg can claim to be the leader who broke the political consensus, asking some hard questions about the course of the conflict. It will be hard to paint Clegg as a softie without a full frontal assault on the Lib Dems, which Cameron shied away from in the first debate. Meanwhile Clegg will be able to muck in with Cameron in attacking Brown over equipment.
3) Europe — Upper hand to Cameron
Most people strongly disagree with Lib Dem policy on Europe. The problem for Cameron is how far to push it, given an obsession with Europe has backfired in past elections. Cameron will know he has to make the running himself because Brown is unlikely to do it for him. Clegg may be a euro-loving former MEP. But he knows what is wrong with Europe and can give a reasonable account of how it should change. Meanwhile Brown will be looking to knock down Cameron if his anti-Europe message goes too far. This will be a tricky balancing act.
4) Trident — Upper hand to Cameron
The Lib Dem position on Trident leaves them open to attack. Brown and Cameron will both be looking to land a knock out punch. The Lib Dems say they will scrap the Trident system but have not decided on an alternative, which can look like dangerous equivocation. Unilateralism is unpopular. In Clegg’s favour are polls showing the public is split over Trident. He can also turn it into a matter of being honest about the deficit. And finally there is Clegg’s killer weapon: the fact that his position is supported by General Sir Richard Dannatt — Cameron’s own adviser on national security.
5) Iran — Upper hand to Clegg
Both Cameron and Brown will want to appear as tough on the Mullahs. A more nuanced Clegg position, warning over the dangers of precipitous military action, will stand out.