ARG has had a pretty unreliable record this primary season. But this is a pretty stark shift. ARG's Pennsylvania poll taken on April 5-6 had a Clinton-Obama tie at 45%. Today they have a new poll out, taken April 11-13, shows a 20 point spread. Clinton 57%, Obama 37%.

As a control, the two national tracking polls seem to show no discernible shift. Rasmussen's held steady since the 11th, with a small and statistically insignificant increase for Obama. Gallup's has also been essentially static. But their number for today has yet to be released. But it's also true that coverage of this story in Pennsylvania has likely been as intense as anywhere in the country.