however, it's extremely unlikely that voters in maine are going to take out their frustrations against trump, which may be real, by voting against susan collins. there is no logic in that. it wouldn't make any real difference, it would just be undirected hot rage. in fact, there's a reason she keeps winning, and it's the same reason bernie sanders keeps winning, it's a reflection of that part of the country's dislike of both parties. it may be a two party system, but that isn't necessarily what americans actually want, and frustration with trump doesn't necessarily translate into support for democrats, who may support gun control or have views on climate change that are not welcome in the region. it's just not that easy.
elections are complicated things. you can't really explain them fully until after they happen.
but there is no empirical indication that susan collins is at risk of losing her seat.