According to a new study by the liberal group Third Way, pollster assumptions in the swing states may be very, very wrong.  While many pollsters — like CBS/NYT/Quinnipiac and PPP, just to name two — assume that the electorate model for Tuesday will be similar to 2008, the Third Way study on partisan registration in eight states shows something very, very different.  In each of these states, Democratic registration has trailed that of independents and Republicans by significant amounts — and in six of the eight states, Democratic registration has declined, sometimes dramatically (via Politico’s Morning Report):

In total, since 2008 in these 8 states:

• Independent registration has increased 969,589, or 14.4%, and now stands at 7,697,565;
• Republican registration has increased by 158,037, or 1.3%, and now stands at 12,047,112; and,
• Democratic registration has decreased by 372,827, or 2.5%, and now stands at 14,723,535.

Democratic registration was down over 800,000 in our August voter registration report. Since then, Democrats have added 427,502 to the voter rolls just in these 8 states.

In 6 states—Colorado, Florida, Nevada, New Mexico, North Carolina, and Pennsylvania—Independent registration has grown faster than either Democratic or Republican registration. In Iowa, Republicans gained while Democrats and, to a lesser extent, Independents fell. In New Hampshire, voter registration fell across the board, but Republicans shed the fewest voters. And in 5 states—Colorado, Florida, Nevada, New Mexico, and North Carolina—Independent registration increased by double digits, the largest a gain of 25.2% in Colorado and the smallest 19.5% in Nevada.

Their chart shows the problem for Democrats in stark relief:

Recall that the response to the fact that Romney has consistently led nationally among independents (although not always in each state) has been that independents are proto-Republicans that shed their party identification.  At least in these swing states, that appears to be more true of Democrats rather than Republicans.  Overall, Republican identification has slightly increased, while Democratic identification has declined over the last four years.  That corroborates Gallup findings that Republican and Democratic identification has equalized in the population.

This chart shows the folly of assuming that the 2012 electorate will look like 2008’s, especially in these swing states.  And I suspect that this same dynamic has taken place in most of the other 42 states, too.  If Romney’s winning independents and Republican registration has gained a net 3.8% over Democrats in the last four years, that looks dispositive.

Update: Babalublog has more on Florida’s numbers.