(McCain, light green, Obama, dark green
Voter preferences have been closely divided between Obama and McCain in each of the last three individual nights of polling, underscoring the notion that the race has tightened for the moment. This could to some degree reflect Obama's absence from the campaign trail while he vacations in Hawaii. He will return to the spotlight over the next few weeks upon naming his vice presidential running mate and accepting his party's nomination for president at the Democratic national convention, and both events have typically been associated with a bounce in support for a presidential candidate.
On Thursday, the Obama and Hillary Clinton campaigns announced an agreement to put her name into nomination for president at the convention. Given that the race has been tight for the past few days, it is unlikely this announcement is related to any change in Obama's support.
Since early June when Obama clinched the nomination, he has averaged a three percentage point advantage over McCain in Gallup Poll Daily tracking. (To view the complete trend since March 7, 2008, click here.) -- Jeff Jones