First Night: The Vertical Hour, Music Box Theatre, New York

New York is the city where David Hare performed one of the bravest and most admirable feats of his distinguished career. In the late 1980s, he publicly rebuked (in an advertisement purchased at his own expense) the theatre critic of The New York Times. Given that the incumbent has make-or-break power over theatrical life in the city, Hare's exercise was akin to inviting God to step outside and settle a dispute on the pavement.

Frank Rich (for it was he who was then the man in the stalls for The New York Times) has since evolved into one of the best liberal political/cultural columnists of the age. He was among the first slender band of people to come out against US policy towards Iraq and against the President at a time when, post-9/11, taking a stand against patriotic pieties was by no means a safe or easy business. It would be nice to imagine that these ancient enmities could now be soothed into submission by a drink and a swapping of shared views - for Hare and Rich are, most persuasively, on the same side.

And now New York is the city to which Hare has given the premiere of his latest work, The Vertical Hour. It is unveiled here - in Sam Mendes's clunking production - rather than in London because Hare is peeved with our own National Theatre. His last play there, Stuff Happens, which presented the Iraq crisis from the perspective of the moral tragedy of Colin Powell, was too expensive (because of the size of cast) to transfer to the West End. Hare therefore wanted to extend its run on the South Bank. But there was too much in the production line (all of it good) to permit this. So Achilles sulked in his tent and took his next labour, in a cloud-capped towering huff, to New York.

The Vertical Hour is not a good play, though it expresses certain views with great crispness and force. Julianne Moore - a hennaed, pale, tensile presence - is not a natural stage actress but she does what she can with a very difficult role, even if she often comes across as an awkward student rather than the powerful academic she is supposed to be.

Hare once intervened in the debate about high and popular art - the question tendentiously simplified to the false opposition: who is better, John Keats or Bob Dylan? Ironically, watching The Vertical Hour, I was constantly reminded of Keats's profound view that we dislike art that has "a palpable design" upon us. The whirring mechanism in The Vertical Hour almost deafens you to the moment when the play works as drama not polemic.

Bill Nighy, the "thinking woman's crumpet", is accorded little chance to demonstrate his sex appeal in a play where he is a philandering doctor with a son (uncomfortable Andrew Scott) who has defected to the United States as a kind of upmarket Hippocratic-oath-taking personal trainer and who returns to show off his new, older girlfriend - a former war reporter turned Yale academic (Moore) - to erring, supposedly magnetic papa. What follows is an honourable attempt to create a debate in which the personal and the political become painfully inextricable. Apart from one or two brilliant moments, it fails.

We need a play that burrows deep into the nervous system of a bright person who sincerely thought that the invasion of Iraq amounted to "liberation". We need a play that sees Western indulgence through the eyes of someone from the West who is more of a Muslim cast-of-mind than she knows. We need a play that says the knee-jerk antipathy to everything that America has done in the past five years could do with some vigorous questioning. But the toxic combination of George Bush and Tony Blair engender a crudity of response.

The Vertical Hour is better than the latest plays by Caryl Churchill and Sam Shepard and it may be one of those works that will mean more 10 years from now. At the moment, though, what one registers is disappointment.