New England rats might dominate a small nearby state like New Hampshire, but so far as the state level is concerned, I believe they get largely absorbed. Sure, a county here and there will get overrun.
And they give us the joys of congress critters like Debbie Wasserman and Ted Deutch.
It will be more difficult for NH liberals to gain a permanent foothold because the government jobs just are not there like they are in Vermont, Massachusetts, Connecticut, etc. The demographics work agains them as well in the Granite State, moreso than in Rhode Island or Massachusetts.