There#s one slight problem with that... Vermont has a higher percentage born in the state than... say... Connecticut or New Hampshire. ie Vermont hasn't (primarily) changed due to immigration, but to realignment. In fact, New Hampshire would probably be a lot more like Vermont if it wasn't for the many upper-class immigrants from Massachusetts.
The interesting thing is that Vermont is a far poorer state than Massachusetts, yet its liberalism seems to be more socially based than economically based.
Clearly, there has been a major realignment. People are voting more on social than economic issues now, though as I said, Massachusetts and Rhode Island, in particular, still have a lot of the old-line economic liberals. Vermont seems to be an example of an inbred state that is largely imploding due to isolation from reality and willful separation from the modern world. In its own way, it seems to be becoming like the old pre-civil rights south.
How is Vermont imploding? How is it like the pre-Civil Rights South? Are there lynchings? Do people live with the threat of armed mobs and riots? Do we have Vermonters threatening to leave the Union? Also, here you describe Vermont as inbred and isolated, yet in other threads you have described it as full of immigrants from the urban NE. Which is it?