The Prime Minister will also face comparison with his host. He will speak little more than a week after the US President addressed an assembly of both Houses. Mr Obama did what we know he can do, almost without effort. He spoke faultlessly, stirringly, pointedly and passionately. It would be a mistake to reach for rhetorical power in imitation. Even if the writing is in the same class, which is doubtful, the delivery never will be. That is not a criticism of Mr Brown. The same would be true of any other leader of a developed country.