A few days ago Gallup released some composite data culled from polling over the past three months. The partisan self-identification numbers show a remarkable thing: Voters give the Democrats their greatest edge in over a decade, and tied for their greatest advantage in 20 years.

While the percentage of independents shrunk a bit since late 2007, Gallup trends show relatively little change in Americans' identification with the Republican Party over the same period. This has generally held at 27%, while Democratic identification increased from 31% at the end of 2007 to 36% today.

This skew toward one party in the redistribution of voters in an election year is not unprecedented. However, by the third quarter (from July to September) it would be unusual not to see some heightened public identification with both parties. If the percentage of Americans identifying themselves as Republican does not pick up, the Democrats will have their strongest structural advantage in 20 years going into the November election.

[...]

The Democratic Party entered the 2008 election season with a solid advantage in party identification (32% to 27% in the fourth quarter of 2007), but, as a result of independents becoming more partisan in their thinking during the election, the Democrats now lead by a larger nine percentage point margin, 36% to 27%, tying with the third quarter of 1997 for their widest advantage in the past 20 years.

Why is this number so important? Back in the fourth quarter of 2006, the Democrats held a 6-point advantage in self-identification en route to a roughly 7-point victory in the overall popular vote for the House of Representatives. In 2004, Gallup actually found that Republicans had a self-identification edge, a data point that cannot be separated from George W. Bush's 3-point victory in the popular vote that fall.

Does this mean that the Democrats will necessarily have an overwhelming advantage on election day, or that Barack Obama is a shoo-in for the White House with numbers like these? Of course not. Even as partisan self-identification numbers aren't entirely malleable, they do tend to shift slightly as election day approaches and voters harden in their views. Nevertheless, these numbers do underscore a key point that is not really breaking through the media narrative at this juncture: Obama and the Democrats are ahead right now; this is not a tied race.