Most surveys conducted during the 2012 U.S. presidential campaign showed large swings in support for the Democratic and Republican candidates, especially before and after the first presidential debate. …
We conclude that vote swings in 2012 were mostly sample artifacts and that real swings were quite small. While this account is at odds with most contemporaneous analyses, it better corresponds with our understanding of partisan polarization in modern American politics. CONT.
Andrew Gelman, Sharad Goel, Douglas Rivers & David Rothschild, Quarterly Journal of Political Science
See also: 2012 presidential trial heats