STEVE INSKEEP, HOST:
The political map of America changes, but it doesn't change very quickly. Massachusetts was a reliably liberal state decades ago and still is. The South is still the South. This raises the question of why it is that certain areas come to be reliably liberal or conservative.
NPR Shankar Vedantam joins us to discuss some research that explores the question. Hi, Shankar.
SHANKAR VEDANTAM, BYLINE: Hi, Steve.
INSKEEP: What's the research?