From The Polling Report archives:
Pundits and prognosticators, strategists and seers all said it couldn’t be done. Incumbents who garner positive ratings from fewer than four in ten voters and who post double-digit deficits in match-ups against opponents (in public polls) are not supposed to win—and they usually don’t. In fact, combing through the history of polling it is hard to find someone other than Senator Harry Reid who accomplished that feat.
Three prime factors account for this history-making result: CONT.
Mark Mellman (Mellman Group) & Jim Margolis (GMMB), The Polling Report