Many people are talking about the dramatic tightening of the Pennsylvania Senate race between Republican Pat Toomey and Democrat Joe Sestak. But upon closer inspection, most of that apparent tightening seems to be a mirage.

The sense that Toomey’s lead has substantially narrowed is based on three polls:  one by PPP, which shows Sestak up 1; one by Quinnipiac, which shows Toomey up 2; and one by Morning Call Tracking, which shows a tie.  These are the only polls that have been released since Rasmussen showed Toomey to be up 10 points just a week ago.  However, all three polls appear to have significantly under-sampled the very voters who will likely put Toomey over the top.