A successful presidential convention can give the nominee a five- to 10- percentage point bounce in opinion polls. But as Barack Obama and running mate Joe Biden chart their course across the swing states of the mid-west towards Denver on Wednesday, a large chunk of media attention will be eaten up by Hillary and Bill Clinton.

Many supporters of Mr Obama express private anguish over the prominent role he has conceded to the former president and first lady on three out of the four days of the convention this week. The democratic nominee starts off the convention with an insignificant 1- to 2- percentage-point lead over republican rival John McCain.