i don't remember having seen anyone link to this----i'm not sure that doing so here means that there's a disagreement (though there is, really)---but anyway, here's obama's 2007 article "renewing american leadership" in the journal "foreign affairs"
Foreign Affairs - Renewing American Leadership - Barack Obama
it's interesting, particularly if you want an idea of just how centrist obama is inclined to be--and of how skewed the (still) current sense of left-right distinctions are in american politics--that obama could be understood as a "radical" is beyond me.
regardless, this is a pretty comprehensive piece, some of which of course we've now heard before...