Massachusetts' state legislature is heavily Democratic (they currently hold supermajorities in both chambers), and because of that voters are willing to elect liberal Republicans to put a check on them.
Exactly this. The State Party is still a Rockefeller one; it never got aboard the Religious Right train that derailed the GOP federally in New England by association; people around here still distinguish federal issues from state ones.
Also, back to OP, they DID vote for Reagan in 80 and 84 and elected Ed Brooke and Scott Brown to the Senate, all in many of our lifetimes, so it's inaccurate to say "never."
