The only two years where there was not major movement in the Gallup poll of registered voters relative to the final result was 1988 and 2008. Otherwise, we see pretty substantial breaks in one direction or another – in some years, like 1972, 1984, and 1996 the leader has enough of an edge to endure the rise of his opponent. In other years, like 1968, 1976, 1980, 2000 and 2004 we see enough movement that the entire race is turned inside out.
Again, this should make sense in the context of the first chart: When you have upwards of a third of voters making their final decisions this month (or early November), is it any surprise that the polls swing so wildly?
In other words, Obama’s lead of 6 points among Gallup’s registered voters (or his lead of 2.5 points in the recent, reliable likely voter polls) is great to have, but at this point is by no means determinative.