BOSTON — When Michelle Wu first ran for Boston’s City Council, she made get-to-know-you appointments with a series of political rainmakers, and found that their questions took on a familiar pattern.

Where did you grow up? What neighborhood? What neighborhood were your parents from? It took a while for Ms. Wu, the daughter of Taiwanese immigrants who moved to Boston as a Harvard undergraduate, to understand what she was really being asked: Which tribe do you belong to?

In the six years that Ms. Wu has served on the Council, swift change has come to Boston, whose middle-income Irish-American and Italian-American neighborhoods formed the bedrock of a Democratic machine for most of the last century.

Rising housing costs have squeezed out families whose political loyalties had been nailed down, often through patronage, for generations. They have been replaced by transplants, immigrants and professionals who, like Ms. Wu, cannot claim membership in any of Boston’s tribes.