“The imagination of the suburbs is stuck in a model that emerged in Orange County in the 1960s: Goldwater-Reagan voters, white-collar, conservative activists,” said Matthew Lassiter, a University of Michigan historian who has also studied suburban voters.

By contrast, Orange County’s 39th Congressional District today is one of the most diverse in the country. The demographic change that Democrats hope will advantage them nationally — as long as Republicans continue to seem uninterested in courting minorities — is already well underway in these places.

Today Democrats are benefiting from both the changing nature of the suburbs and the changing preferences of white college-educated voters there who are repelled by the president. But the second trend is more precarious for Democrats.

That’s because, as the political scientist Jefferey Sellers puts it, many suburban voters tend toward an eclectic mix of preferences that can seem contradictory. Particularly in denser, close-in suburbs, voters tend to be more cosmopolitan than in rural areas and turned off by culture-war issues that animate other Republican voters. But they’re also more fiscally conservative than many urban voters, and opposed, for example, to the higher taxes some liberal policies would require.

Rural and urban America clearly have distinct politics, one emphasizing individualism and limited government, the other shared commons that require bigger government. (It’s not entirely clear, though, whether these environments shape people’s politics, or if people choose to live in them because of their politics.)

In a sense, suburbia has its own politics, too. Many voters there are motivated to keep taxes from rising and to protect the benefits — good schools, open spaces, stable property values — that attracted them to the suburbs in the first place.

“Moving into these environments, the political identities that move to the fore are not Republican or Democrat, or conservative or liberal,” Mr. Lassiter said. “They are homeowner, taxpayer and school parent.”