In 2008, Democrats had a 7-percentage-point advantage in party identification over Republicans, which was close to the final margin of victory Obama had over Sen. John McCain (R-Ariz.).

Newhouse and other Republicans say it’s foolish to expect a similar proportion of Democratic voters in 2012. They argue a smaller proportion of Democrats are likely to come to the polls in November, while a larger proportion of Republicans eager to deny Obama a second term can be expected to vote.

Polls that assume the makeup will be the same as 2008 don’t take this into account, they say.

“You had an extraordinary 2008 turnout among rural evangelicals, but Republicans stayed home in larger numbers,” Newhouse said. “This time you have a more enthused and energetic Republican electorate, and because of that, you’re not going to see the margins go up, you’ll see it narrow. So instead of a 7 [percentage-point advantage for Democrats], I anticipate something smaller than that.”