Behind Obama's 21-point lead

Tom Jensen says Public Policy Polling has expanded its turnout model.

The Democratic pollster told Dome one reason behind the 21-point lead for Barack Obama in its latest tracking poll is that the firm is now calling voters who cast ballots in the 2004 primary, 2006 primary of 2006 general election.

He called that the "circus turnout model," saying it has worked better in other high-interest races  in Wisconsin, Texas and Ohio.

"I think part of the bump is due to that because it reflects folks who don’t usually vote in primaries being drawn to Obama," he wrote in an e-mail.

Jensen said timing was also a factor. The last poll, with Obama only ahead by one percentage point, was on the worst day of the controversy over Rev. Jeremiah Wright.

Since then, Obama gave a big speech on race and earned a lot of media in North Carolina.

"I think those things could make a large impact on their own," he wrote.