Everyone should read Ronald Brownstein's fascinating cover story in National Journal. Here's the crux of his argument: 

From New Hampshire to California, and from Arizona to Wisconsin, exit polls from this year's contests show the Democratic coalition evolving in clear and consistent ways since the 2004 primaries that nominated John Kerry. The party is growing younger, more affluent, more liberal, and more heavily tilted toward women, Latinos, and African-Americans.

Which means:

This year's changes have accelerated a clear movement away from key elements of the historic New Deal coalition on which Hillary Clinton has based her candidacy.

On the whole, this should count as good news for Democrats because they are expanding their coalition with groups that are becoming an ever-larger share of the voting population. But what does it mean for Barack Obama, who has at times struggled with working-class and older Democrats? As Daniel Larison, commenting on some fascinating new Pew data, notes:

Not only do Democratic defections nearly double in a McCain v. Obama race, but Obama loses a fifth of white Democrats to McCain, and he runs seventeen points behind Clinton among <$30K earners, reflecting continuing weakness with downscale voters. Compared to Clinton, he also loses 14 points among Democratic women, which is a much larger figure of disgruntled women voters turning away from the Democrat and backing McCain than the three-point difference between Clinton and Obama among black Democratic voters.  

Most remarkable of all is that Obama is weaker among Democrats in all age groups than Clinton.  He is four points weaker, and McCain five points stronger, among Democratic voters aged 18-49 than in a Clinton v. McCain race.  The losses are even greater among Democratic voters 50-64 and 65+.  Democratic defections increase across income groups as well.  Obama does much better in the younger age groups among independents, but if the Democratic numbers are any indication this seems to have less to do with age than with style.  Probably the same thing that makes Obama attractive to independents (he doesn’t always sound like a regular Democrat) is what is undermining him with Democratic voters.

And yet in the same poll, because he is so much more popular with independents, Obama does better against McCain than Clinton does. Which has Larison asking:

What happens when these independent voters find that Obama is offering little more than rehashed liberalism and the “post-partisan” fantasy is revealed as just that?

I suppose this could be a problem, but it seems just as likely that Obama will gain ground with the Democratic voters mentioned above once he wraps up the primary. Still, if we assume that he'll do worse on election day with older and downscale Democrats than previous nominees did, the crucial thing to ask is where this will hurt him. After all, the popular vote winner does not necessarily become president. Unfortunately for Obama, Pennsylvania and Florida have significant proportions of older voters, and Ohio has a lot of blue-collar Democrats. We'll have to see what the numbers look like in a few weeks, when presumably he will have consolidated Democratic support.

--Isaac Chotiner