Two new polls give Mitt Romney the edge

Among these is Jon Cohen at the Washington Post, who sees the field as fluid and is willing to credit a large shift in party identification due to the debate performance.

"The recent hullabaloo about adjusting samples (or, in the parlance of pollsters “weighting”) to pre-determined partisan splits," Cohen wrote, "misses that movements in party identification can be just as real as movements in voting intentions."

"These polls show more people are now identifying as Republicans in the wake of Romney’s debate performance. Just as they showed a clear Democratic tilt earlier in the fall, and in the immediate aftermath of Romney’s “47 percent” comments. Shifts happen in the electorate. The only constant is change," Cohen wrote.

Nate Silver at the New York Times agrees with Cohen, but does question the size of the Pew skew.

"It is probably also the case that Republicans won’t actually have a 5-point party identification advantage in the exit poll on Election Day," Silver wrote. "But it isn’t the pollster’s job to project what will happen on Nov. 6. (That’s my job, instead!) Rather, the pollster’s job is to take the most accurate snapshot of the electorate at the time the poll is conducted. Note that the Rasmussen Reports polls, which (improperly, in my view) adjust for party identification, show very little bounce for Mr. Romney. The party-identification adjustment is causing them to miss the story of the election — just as they were largely missing the story of Mr. Obama’s bounce following his convention."

But this is, of course, precisely the question: is the electorate this volatile, swinging wildly from day to day? Or can we predict within a fairly narrow range how many each party (including leaners) has in their corner, and then make some estimate about enthusiasm to predict actual turnout?

In fact, political scientists have long told us that voters are fairly predictable in their partisan voting patterns, even if they claim to be independent.

That is why some polls ask about typical voting patterns and then "squeeze" voters, reducing the number of independents. The Politico/GWU poll released Monday did this, finding only 16 percent independents.

That poll had a D+4 sample, which is roughly between recent highs and lows. But it also found Democrat enthusiasm down and GOP enthusiasm up, suggesting that the final turnout would slide closer toward even if nothing changed.

Assuming that both parties are equally successful in retaining their voters who do turn out, then the closer the partisan split grows toward even, the more the independent vote will be decisive, and most polls currently show Romney with a lead among independents.