The big question tonight: Is Obama's strong showing in Virginia a sign of an expanding coalition, or is it the predictable result of a contest waged on favorable terrain? The answer is probably a little of both. For example, Obama basically tied Hillary among white voters in Virginia* after losing them by 18 points in Missouri, a state he barely won last Tuesday. On the other hand, Virginia has a lot more affluent white liberals and moderates than Missouri does. The majority of them live in the populous DC suburbs, which Obama carried by a 62-38 margin.
Still, I think there are a couple of places you can find genuine growth for Obama. The first place I'd look is older white voters. In Missouri, Hillary won white voters above age 60 by a 67-28 margin. In Virginia, she only won them by a 57-42 margin. That's a 24-point swing toward Obama among a very significant bloc (25 percent of the Missouri electorate; 17 percent of the Virginia electorate).
Another place to look is white Catholics, also a key demographic (16 percent of Missouri voters; 12 percent in Virginia). Hillary won them 50-46 in Missouri; Obama won them 49-48 tonight. These voters aren't just important in Democratic primaries; they're a general-election swing group, too. So it's a doubly-encouraging development for him.
Obama also carried the 5 percent of Virginia voters who were Hispanic by a healthy 54-46 margin. Now, there may be qualitative differences between Virginia Latinos and Latinos in, say, California. (My understanding is that a relatively high fraction of Virginia Latinos have Central American rather than Mexican roots; vice versa for California; there are probably also differences between Hispanic communities that represent 25 or 30 percent of a state's population and Hispanic communities that only represent 5 percent.) Still, this does give lie to the idea that Obama can't compete among Hispanics, which is an important talking point if nothing else.
Finally, CNN unfortunately hasn't broken down its data by both race and income. But, if you look only at income, Obama improved his showing among people making under $50,000 from 51-46 in Missouri to 62-36 in Virginia. While Virginia has about two-thirds more African Americans than Missouri, which could explain some of that movement, it's a big enough swing that I suspect Obama improved among the white working class, too. If true, it would be another real sign of progress. (I'll update you later if I can get the finer data.)
*As always, note that exit polls get updated throughout the evening, so some of these numbers may be off by the time you see them. I'll try to update them before I sign off. [Exit poll numbers updated--11:41 PM.]