TV debates were the defining element of the last election. Cleggmania was born after millions tuned in to the first leaders' debate and were introduced to a politician capable of using voters' first names and looking down the barrel of the camera during his closing statement. Being "televisual" matters more for politicians than ever before.
Tonight is the second televised hustings of the Labour leadership contest on Channel 4 News. It follows the disappointing Newsnight hustings in June, when Jeremy Paxman stole the show. Paxo dominated proceedings and conducted a speed-dating version of his confrontational interview style, taking few questions from the audience of former Labour voters that the production team had assembled in the studio.
Channel 4 is not going to have a studio audience, so a lot rests tonight on how Jon Snow chairs the debate. Ed Balls was said to have been frustrated by Paxman's inability to stop the Miliband brothers jumping in and talking over each other. The formal Labour hustings have used strict rules of engagement, set by the party's National Executive Committee, to stop that happening. Tonight, there will be no holds barred and Snow will be the only referee.
Channel 4's timing is perfect. Newsnight was too early in the contest and BBC Question Time -- on Thursday 16 September -- will probably be too late to affect the outcome. On Sunday, Sky News will broadcast from Ed Balls's home town of Norwich (where Labour lost both parliamentary seats) and has the chance to involve swing voters with the kind of audience participation that has so far been absent from any British political TV debate.
Very early in the Labour leadership election, Newsnight ran a mixed focus group of voters who unanimously backed David Miliband. But we don't know if that was based on their familiarity with him, up against the unelectables and the unknowns. It would be interesting for Newsnight to get the same panel back together after four months and see if they've changed their minds.
When it comes to winning over party members, the veiled endorsements from Tony Blair and Peter Mandelson could not have come at a worse time for David Miliband. His campaign team will have been delighted to have seen today's Mirror front page but dismayed by the "soap opera" and "back to the future" soundbites that are undoing all the positioning of his "post-New Labour" Keir Hardie Memorial Lecture.
Since last Wednesday's article in the Times, David Miliband has lost his voice. Others have spoken for him. The Times itself gave so much top spin to its splash ("Gloves off as Miliband rounds on his brother") that the rest of the week was dominated by others responding to the drawing of first blood.
Tonight is his chance to turn the tide once more because Snow is likely to focus more airtime on him, as the front-runner, and on his brother. The danger for David is that Ed Balls, Diane Abbott and Andy Burnham are increasingly relying on attacking him to gain their own definition, leaving his brother to rise above the fray.
TV debates could still make a difference to this contest, as clips from tonight's Channel 4 News and Sunday's Sky News debates can be embedded in the final round of all-member emails that the candidates send to get out their vote. Having completed more than 50 hustings events, the candidates are familiar with the stock of soundbites that their opponents have drawn on. Tonight, a original killer line could make all the difference.
Richard Darlington is head of the Open Left project at Demos.