Everyone's saying Hillary so I'll say something different: Trump had an appeal in the state (and in other New England states) in 2016 that he just wouldn't have afterwards.
What appeal did he have in New England in 2016 that would quickly fade?
As he had only been a candidate at this point and never held office, he was still seen as a moderate on policy, even if his persona wasn't.
Lest we forget, the Northeastern primaries were effectively a two-man race between Trump and Kasich--that Trump won.