It is being widely assumed that, once we have leadership debates in Britain for the first time, we will have them forever. Perhaps. But there is no particular reason to be certain of that.
There was no US Presidential debate after 1960 until 1976. Thanks to the House of Commons briefing paper, I can report that the first Canadian debate in 1968 was not followed by another until 1979. I don't know if there have been stop-start experiences elsewhere.
And part of the commentariat and political class this morning will be muttering - after the Chancellors debate too - what's the point of having debates if the third party always seems to win them.
It may be hard to row back - but it may not be impossible that a Prime Minister Brown or Cameron in 2014 would believe they could take a couple of days bad headlines by ducking out (just as David Cameron has done on a prime-time BBC1 Panorama interview which every party leader has done in recent electoral history, and where Gordon Brown may now follow suit, though he ought not to).
What we need is a very clear on camera statement from each of the party leaders - and other leading figures in the parties - that they think the debates are here to stay and they will definitely take part, whether ahead or behind in the polls, in any future election.
The traditional way to duck out has been to blame disagreement over the rules of engagement. The format might be improved - but any leader should be willing to take part under the 2010 rules unless changes are agreed.