Using the 141 national likely-voter polls from the Pollster database since July 1st we can examine how the dynamics of the race have changed since the first Presidential debate. So far the pattern looks very reminiscent of the period after the first Presidential debate in 2004 between George W. Bush and John Kerry. In that election, support for Bush dropped about five points after the first debate, leaving the President with a two-point lead that he maintained up until Election Day.. The 2012 Presidential campaign seems to be following the same trajectory except that President Obama no longer has a lead to maintain.
The polls indicate that support for the President fell by about four points immediately after the first debate leaving him essentially tied with Mitt Romney. If the President had reverted to trend at that point and followed the dotted line, he would have gained back a lead in the polls of about 1.3% by Election Day. So far, however, the polling suggests no such return to form. On the basis of the polling since the first debate, the candidates look to remain roughly tied from now until the election.
(These data include the adjustments for “house effects” described in my previous post. The results for the full regression model are here. The later debates show no measurable effects.)