The great sin in contemporary democracy is to give the impression that you are holding something back. We want politicians who are comfortable talking about their inner selves, their private emotions and convictions. At the same time, we cannot stand politicians who appear to be pandering to this taste for self-exposure.
This relentless obsession with personal authenticity is a big problem for our politics. We chip away at the public persona of any political leader, searching for the evasions and inconsistencies that suggest they might be someone with something to hide. In this way, we try to root out the hypocrites.
But it doesn't work - the search for political integrity, couched in the terms of personal revelation, simply breeds cynicism on all sides. The politicians, subject to this kind of scrutiny, don't remove their masks, but instead try to make sure the masks are more securely in place. Meanwhile, the public start to mistrust everything they hear.
There are no winners here. In the US, for example, the primary season began full of hope that this year's candidates might conduct a serious debate about America's future. The likely contenders in the autumn, Barack Obama and John McCain, both have reputations as sincere, relatively honest politicians capable of speaking their minds. But this guarantees only that the campaign will end up as a battle of hypocrisies, as each side is forced to show that the other's reputation for truth-telling is not what it seems. The greater the claims of integrity, the easier it is to make the charge of hypocrisy stick.
So we should recognise that the demand for personal authenticity in politics is self-defeating, and learn to be more tolerant of the inevitable hypocrisies of democratic life. No plausible candidates for high office can be entirely who they say they are, yet every candidate has to pretend to be just that. Attempting to root out hypocrisy just makes hypocrites of everyone involved in the political process - not just the politicians, but the press, which can't possibly live up to the standards of personal revelation that they impose on others, and the public, who can't either.
Saying we need to accept a certain amount of hypocrisy, and stop looking for the person behind the mask, doesn't mean we have to accept every kind of hypocrisy or concealment. In Bri t ain, it doesn't much matter if Gordon Brown - who is constantly being exhorted to tell us who he really is - wants to draw a veil over what's in his heart, but it does matter if he wants to draw a veil over what he has done to the tax system. It is absurd to expect politicians to tell us the whole truth about themselves, but it is reasonable to expect them to tell us some of the truth about politics, with all its inevitable compromises and uncertainties, its losers as well as its winners. That's what we should ask for.
David Runciman is the author of "Political Hypocrisy: the Mask of Power, from Hobbes to Orwell and Beyond" (Princeton, £17.95)