Why are the Berkshires in Mass so liberal?

[soniquemd21921]

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Those towns (along with Wellesley, Needham, Dover, Weston, Melrose and Reading) used to all be rock-ribbed Republican well into the 70's. Have the demographics changed in those towns since then? And even Newton, Brookline and Boston's Back Bay neighborhood were strongly Republican until the early 60's.

Do many of the Republicans that now live in New Hampshire "exurbs" like Bedford, Salem, Derry  or Hudson use to live in Concord, Lexington and Wellesley - suburbs that were 70% Republican half a century ago?

[soniquemd21921]

Arlington: 55.0% (1948), 42.2% (1960), 42.3% (1972)
Belmont: 65.1% (1948), 49.2% (1960), 50.5% (1972)
Lexington: 70.7% (1948), 58.0% (1960), 46.5% (1972)
Lincoln: 74.4% (1948), 63.6% (1960), 46.8% (1972)
Concord: 70.5% (1948), 59.2% (1960), 51.1% (1972)
Acton: 77.4% (1948), 69.5% (1960), 58.2% (1972)
Littleton: 72.5% (1948), 58.1% (1960), 56.7% (1972)

And just for fun, I'd like to throw in:

Cambridge: 32.8% (1948), 28.6% (1960), 25.4% (1972)
Amherst: 68.5% (1948), 60.0% (1960), 31.2% (1972)