Stuff Happens, Olivier, National Theatre, London

In his book Bush at War, the journalist Bob Woodward quotes George Bush as telling him that the interesting thing about being President is that you don't need to explain yourself: "Maybe somebody needs to explain to me why they say something. But I don't feel like I owe anybody an explanation."

In his book Bush at War, the journalist Bob Woodward quotes George Bush as telling him that the interesting thing about being President is that you don't need to explain yourself: "Maybe somebody needs to explain to me why they say something. But I don't feel like I owe anybody an explanation."

The line crops up early on in David Hare's play about the run-up to war in Iraq, and might be seen as a kind of warning to anybody expecting Stuff Happens to be a straightforward indictment of American foreign policy. Hare is less interested in telling us whether the war in Iraq was right or wrong - doesn't everybody have a view on that already? - than in exploring the far more problematic question of why it happened at all. In the end, though, all his probing runs into the brick wall that is Bush. It would be easy to caricature the President as an idiot, but Alex Jennings plays him as a sphinx, with blank eyes and a smile determinedly devoid of meaning.

In an area where stark certainties are all too common, Hare's embrace of ambiguity is welcome; and as a demonstration of his grasp of the issues and his ability to empathise even with those whose views he finds obnoxious, Stuff Happens is impressive. But as drama, as a narrative that engages and convinces, it is only intermittently successful. That is partly because of the nature of the subject matter - diplomatic negotiations, cabinet meetings, transatlantic phone-calls: unsurprisingly, Stuff Happens often seems talky and static.

But Hare makes difficulties for himself through the way he mixes fact and fiction. In a programme note, he explains that events in the play "have been authenticated from multiple sources. Scenes of direct address quote people verbatim. When the doors close on the world's leaders and on their entourages, then I have used my imagination." In practice, the distinction is less clear-cut than that sounds: when Donald Rumsfeld says, "I tell you what is legitimate: what we do is legitimate", is that a close paraphrase based on reports by people who were in the room with him, or has Hare invented a form of words to encapsulate one possible interpretation of Rumsfeld's views?

An uneasy liaison between reality and fiction also characterises much of the acting. Nicholas Hytner's cast struggle to find a register that is believable both for the invented, representative characters and real people. The difficulty is acutely visible in Nicholas Farrell's Tony Blair: at times he offers a performance of genuine depth and complexity, at times relaxing into a caricature - triggering laughter from the audience.

As an interpretation of events, Stuff Happens is penetrating and ingenious, and it contains effective moments of high drama and low comedy. But as theatre, it never manages to find momentum: given the talents involved, it has to be counted a disappointment.

To 6 November (020-7452 3000)