Continental Divide, Repertory Theatre, Birmingham

With the Americanisation of British politics proceeding apace, here is an eloquent protest in the shape of two long, densely analytical plays about the grotesque state of US politics written by a British dramatist, David Edgar.

Continental Divide risks the charge of presumption in its energetic, boffin-like approach to the American malaise. It says much for the Oregon Shakespeare Festival and the Berkeley Repertory Theatre that they commissioned the pieces from a Limey. In Tony Taccone's production, unveiled a year ago in Oregon, the plays now reach the author's native heath.

If only some British theatrical institution would sponsor a drama from Tony Kushner about Downing Street's US fixation. But invoking Kushner highlights the limits of Edgar's achievement. Kushner's plays capture contemporary reality at a depth unreachable by Edgar, whose work here is stuck in the 1970s debate play. Characters who are little more than the sum of their political positions address each other like public meetings, relentlessly.

Continental Divide is two interlocking, cross-cast plays. They present us with a fictional, acrimoniously fought election campaign for state governor. In Daughters of the Revolution, we see it from the Democrats' perspective, and in Mothers Against from the Republicans'. But one of Edgar's main points is that politicians of both parties are soulmates, having more in common with each other than the voters in a culture obsessed with spin and soundbites.

Daughters focuses on middle-aged baby boomers and the boomerang effect of the radical actions of their youth, given a muck-raking political climate where candidates can be reduced to the worst thing they ever did. The droll 55th birthday present of his FBI file sends the ex-activist Michael Bern (Terry Layman) on a quest to find out which member of his Sixties cell snitched. This opens up the more general question of why the left almost cyclically betrays itself, and the search accidentally propels him into the world of new-style protest: the single- issue eco-movement, for which Edgar evidently has a soft spot.

The plays imagine a world where a new proposition has been passed, which requires voters to make a dubiously worded oath of allegiance - a commitment not to support any organisation that uses "force".

Set during a brainstorming weekend at the country retreat of the Republican candidate (Bill Geisslinger), Mothers confirms that, for both contenders, public endorsement or rejection of the proposition is not a question of principle, but of what will play best with TV viewers.

It's significant that Continental Divide is at its liveliest when showing us the cynical debate "prep" conducted in private between the contender and a right-wing luminary. Here, the play revels in the "game" it condemns. But elsewhere, there's a fatal lack of human roundedness and inconsistency.

'Continental Divide' is at the Barbican, London EC2, 20 Mar to 4 Apr (0845 120 7511)