For sure, Cameron and Brown will try to do the old 1980s Cold War trick of portraying Clegg as soft on defence. But it ain't 1987, and most of the country has surely moved on. Apart from the kind of people who are persuaded by the ludicrously pro-Tory line of the Sun and the Mail; but then, they're the hardcore Tory voters - 30% of the electorate - anyway. Not the swing voters.
As the only major party who opposed the Iraq war, the Lib Dems also have a big "I told you so" advantage there.
It's quite possible we could see a further boost to Lib Dem polling after this debate - as long as Clegg can do as well as he did last time. It'll be tougher in one way as both Brown and Cameron will be gunning for him more than last time. On the other hand, that gives him the chance to carve out a distinctive position in one of the areas where Lib Dem policy is distinctive - and more progressive - than Labour or the Tories.
If we see the Lib Dems at 38% or so in the polls after this debate - the level at which they start to win hundreds of seats on a uniform swing - prepare for absolute fucking PANIC STATIONS at Labour and Tory central. Although my preference going into the election was for Labour, I'm really rather enjoying this, and would love it if the Lib Dems went all the way into Number 10. A fair voting system after all these years, eh? Who'd have thought it?