According to this piece by Lexington in the Economist, it's not Chicago, but California that has become the new epicenter of the Demcratic party. As evidence, the author cites relatively recent power grabs in Congress--first and foremost by Nancy Pelosi, who won the speakership over the moderate Texan Martin Frost. But Californians also control most of the important committees in the House now, like Energy and Commerce, Education and Labor. Not a bad sweep for a single state, even if it is already pretty big and populous (but as Texas now knows of course, it takes more than geographic size and population to seize important chairmanships in Congress and affect policy).

So the question the author asks, and I think it's worth considering, is whether the Democratic party is in danger of being "captured" by California, which has a progressive social agenda, but has pitfalls as well (witness the dysfunctional politics), in the same way the Republicans were "captured" by the South and became a regional party.