Labour was right to turn down Sky News and refuse to televise yesterday's leadership hustings at the meeting of the Parliamentary Labour Party. There are some discussions in politics that are best held behind closed doors, and in their attempts to appeal to MPs the candidates have to be mindful of what the media are reading into what they say.
Until Wednesday night, when nominations close and the New Statesman hosts the first open hustings in Westminster, Diane Abbott, Andy Burnham and John McDonnell may well be tempted to throw caution to the wind to try to get on the ballot paper.
However, serious candidates need to mind their language and beware the temptation of saying one thing during this election, if they are likely to end up saying something different at the next general election. Labour made great use of quotations from transcripts of what David Cameron said when he ran against David Davis, and you can be sure that CCHQ's media monitoring unit will spend the long, hot summer filling away ammunition that Cameron can use at PMQs when he faces the new leader of the opposition come October.
Abbott and McDonell have almost nothing to lose in the rhetorical arms race. Even if they can get on the ballot paper, you wouldn't expect them to serve in the team of "Andy MiliBalls", given that they have been so quick to condemn their backgrounds, the role they played in making New Labour an electoral force and their numerous achievements in government.
These things matter, because the left is debating not who should be our fightback figurehead, but who should be the left's candidate for prime minister. Jon Cruddas's decision not to run shows that he understands this, and his tone in the 2007 deputy leader election was marked by its focus on ideas and policy.
Being prime ministerial has to start now, and all the candidates need to mind their language. So, when David Miliband tells the GMB conference that he was responsible for Building Schools for the Future, while Ed Balls is in parliament opposing Michael Gove . . . Or when Ed Balls tells the Guardian that he hasn't travelled round the world, so he's more in touch with Britain . . . Or when both Eds reopen a divisive debate on Iraq during Saturday press interviews . . . They are all experienced political operators and know that when you swing your elbow, journalists always make sure it lands on one of your opponents.
But minding your language doesn't mean ducking the issues.
So when Ed Balls writes in the Observer, advocating a change in future immigration policy and an analysis of a decision back in 2004 that with hindsight he thinks the Labour government got wrong, he deserves some credit. Of course, he is appealing to the left and to the unions. And yes, his position rightly gets characterised as protectionist in the Times. But this weekend Balls went one step further than Ed Miliband, who was first to identify immigration as "a class issue" in his speech to the Fabian Society that launched his candidacy.
Andy Burnham may be unashamedly proud to call himself the "continuity candidate", but if he does get enough MPs to nominate him, he and David Miliband will need to address the issue of immigration and the associated policy problems of welfare reform, social housing and fair distribution of scarce resources by the state.
Labour's leadership election needs to be about policy issues and big ideas, not just about values and character. The left needs an open debate about our direction and it needs to start with candidates showing leadership by saying what they would do differently. If the candidates don't disagree, that direction will not become clear and Labour will lose again.
But, for the good of the party and for the sake of everyone who needs a government of the left, the candidates' disagreements need to be about positive policy prescriptions and not petty personality politics.
Richard Darlington is head of the Open Left project at Demos.