Barack Obama leads John McCain in Gallup Poll Daily tracking interviewing conducted Wednesday through Friday by an identical 52% to 42% margin among both traditional likely voters and expanded likely voters. Obama leads by a similar 52% to 41% margin among all registered voters.
This is the first time since Gallup began estimating likely voters in early October that there is no difference between Gallup's two likely voter models. Obama's lead of 52% to 42% using Gallup's traditional estimate of likely voting criteria takes into account past voting as well as current intentions. Obama's identical lead using the expanded model takes into account only current voting intentions.
I'm having a hard time thinking of any particular reason why what was a 2-point race on Monday should have swung so strongly in Obama's favor in the span of five days. If this Gallup swing is real -- if a tsunami of late-deciding voters pushes Obama to a double-digit win -- the likely explanation will be bandwagon psychology. The marginal undecided voter wants to vote for the winner.