Who speaks for Wales?
An interesting pre-debate debate has opened up about who speaks for Wales.
Tonight's event is obviously a great opportunity for Plaid Cymru.
This is the first time its leader Leanne Wood will be on the top table in the only occasion in which David Cameron and Ed Miliband will appear together during the entire campaign.
It's the kind of exposure party spin doctors could only have dreamt about and the first thing she's likely to say is how she represents Wales.
In other words she'll try to blur the lines between Plaid and the country itself.
Unsurprisingly the other parties have got in early and got in hard.
Welsh Labour has described Plaid as a minority party at every level of government, and have happily trotted out the statistics revealing the uncomfortable truth for Plaid that it is the only one of the smaller parties not to have seen any kind of significant bounce in the polls since 2010.
Even though Ed Miliband will be centre-stage, Welsh Labour is clearly acutely aware of the potential benefits to Leanne Wood.
After all, on the day that the Plaid leader will be standing between Ed Miliband and Nicola Sturgeon, claiming to be the voice of Wales in a TV debate watched by millions, the First Minister Carwyn Jones, the man who travels the world representing Wales, is left to blog in the Huffington Post. Incidentally neither of them are standing in the election.
It's not only Labour - the other parties have all weighed in as well on the issue of who represents Wales.
Plaid Cymru needs the exposure and a strong performance from its leader tonight because, as Labour has reminded everyone, the polls have not suggested any meaningful rise in support for it.
Its campaign strategy has been geared around this debate. Plaid has front-loaded its campaign, with two launches already out of the way, to take as much advantage as possible from the event.
Its big job then would be to try to maintain the momentum over the next five weeks.
It must surely be the case that Leanne Wood has had more UK-wide exposure than any of her predecessors, but can she take advantage of it to really take Labour on in places like Llanelli and Anglesey, or at the very least lay the foundations for a strong performance in the assembly elections next year?
Time is obviously going to be limited in the debate. I suspect the biggest danger for Plaid, and for the other party leaders as well for that matter, is to go missing in action if the debate turns into a bunfight as it opens up in the latter stages.