State of the race: Obama's biggest lead yet is reminder of the shifts in partisan breakdown and of the long odds McCain faces

A new national poll released by Newsweek this evening ensured that the media finally have a data point to cite when insisting that Barack Obama is enjoying a post-nomination bounce:

• Barack Obama leads John McCain by 15 percent, 51% to 36%. This includes 80% of the vote of registered Democrats and a 12% lead among independents.
  
• The poll does note that, while John Kerry led George Bush by only 6% at this stage four years ago, Michael Dukakis was ahead of George H. W. Bush by double-digits at the end of June of 1988.

There are no other national polls even coming close to Newsweek's finding, which for now is more of an outlier. And it would be entirely point out that large leads 5 months before to the election mean nothing. But what does mean something, what is truly fascinating and is not an outlier, in this survey is the sample's partisan breakdown: 55% of respondents identify themselves as Democrats and 36% as Republicans.

Under normal conditions, such a breakdown would be too unrealistic to taint the poll's results. Not in 2008. All pollsters are finding a shift in voters' allegiance towards the Democratic Party, though the size of that shift varies in different surveys. This will be the key measure to look at in the coming months. While a 19% advantage for Democrats might seem excessive, most of SUSA's state polls are finding a swing of 10 to 15% compared to 2004's exit poll.

If Newsweek's and SUSA's findings are at all correct, it means that Democrats have gained such a gigantic advantage in partisan affiliation that it will be nearly impossible for McCain to win this election. Voters' partisan identification will not change over the next 6 months, and they reveal the enormity of the task of hand for McCain to put together a winning coalition: He has to maintain Bush's margin among registered Republicans while significantly distancing Obama among independents and also capture a substantial share of the Democratic vote.

If McCain fails to do live up to any of the part of this equation, he will be buried by 2008's overwhelmingly anti-GOP environment.

The good news for the Republican candidate: He has been able to put the pieces together in most polls that had been released up to this week, enjoying cross-over Democratic support and a slight lead among independents. This shows that McCain still seems like enough of a maverick to over-perform his party and no doubt poll better than what any other Republican nominee would have been able to.

The bad news for McCain: Obama is now increasing his support among registered Democrats -- and that alone could put the election out of reach. This is the Republicans' key disadvantage this election: Given how much the ranks of registered Democrats have increased, this election will be played out among that constituency more than among independents. (Almost) all Obama has to do is defend his home turf; McCain has to seduce the opposite camp.

That it is Obama who is looking to expand the map to traditionally Republican states like North Dakota, Indiana and Georgia is thus understandable cause for panic for the GOP. Obama does not need the support of cross-over Republicans, but by putting McCain on the defensive he will force the Arizona Senator to protect his base while the vote of registered Democrats remains less contested.

Given the structural obstacles McCain is facing this year, what is surprising is that he is trailing by 15% in only one poll. It is a testament to McCain's electoral strength that he is remaining competitive in most surveys that are being released and that Obama's post-nomination bounce has for now been limited to a few points. But in the end, McCain is dragged down by Bush in 2008 just as much as he was in 2000.